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This commit adds a kthread-creation callback to the
_torture_create_kthread() function, which allows callers of a new
torture_create_kthread_cb() macro to specify a function to be invoked
after the kthread is created but before it is awakened for the first time.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Cc: Dietmar Eggemann <dietmar.eggemann@arm.com>
Cc: Josh Triplett <josh@joshtriplett.org>
Cc: Juri Lelli <juri.lelli@redhat.com>
Cc: Valentin Schneider <vschneid@redhat.com>
Cc: Dietmar Eggemann <dietmar.eggemann@arm.com>
Cc: kernel-team@android.com
Reviewed-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Acked-by: John Stultz <jstultz@google.com>
In kernels built with CONFIG_PROVE_RCU=y (for example, lockdep kernels),
the following sequence of events can occur:
o rcu_init_tasks_generic() is invoked just before init is spawned.
It invokes rcu_spawn_tasks_kthread() and friends.
o rcu_spawn_tasks_kthread() invokes rcu_spawn_tasks_kthread_generic(),
which uses kthread_run() to create the needed kthread.
o Control returns to rcu_init_tasks_generic(), which, because this
is a CONFIG_PROVE_RCU=y kernel, invokes the version of the
rcu_tasks_initiate_self_tests() function that actually does
something, including invoking synchronize_rcu_tasks(), which
in turn invokes synchronize_rcu_tasks_generic().
o synchronize_rcu_tasks_generic() sees that the ->kthread_ptr is
still NULL, because the newly spawned kthread has not yet
started.
o The new kthread starts, preempting synchronize_rcu_tasks_generic()
just after its check. This kthread invokes rcu_tasks_one_gp(),
which acquires ->tasks_gp_mutex, and, seeing no work, blocks
in rcuwait_wait_event(). Note that this step requires either
a preemptible kernel or a fault-injection-style sleep at the
beginning of mutex_lock().
o synchronize_rcu_tasks_generic() resumes and invokes rcu_tasks_one_gp().
o rcu_tasks_one_gp() attempts to acquire ->tasks_gp_mutex, which
is still held by the newly spawned kthread's rcu_tasks_one_gp()
function. Deadlock.
Because the only reason for ->tasks_gp_mutex is to handle pre-kthread
synchronous grace periods, this commit avoids this deadlock by having
rcu_tasks_one_gp() momentarily release ->tasks_gp_mutex while invoking
rcuwait_wait_event(). This allows the call to rcu_tasks_one_gp() from
synchronize_rcu_tasks_generic() proceed.
Note that it is not necessary to release the mutex anywhere else in
rcu_tasks_one_gp() because rcuwait_wait_event() is the only function
that can block indefinitely.
Reported-by: Guenter Roeck <linux@roeck-us.net>
Reported-by: Roy Hopkins <rhopkins@suse.de>
Reported-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Tested-by: Roy Hopkins <rhopkins@suse.de>
Use guards to reduce gotos and simplify control flow.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Reviewed-by: Valentin Schneider <vschneid@redhat.com>
Link: https://lore.kernel.org/r/20230801211811.828443100@infradead.org
The sched_rr_timeslice can be reset to default by writing value that is
<= 0. However after reading from this file we always got the last value
written, which is not useful at all.
$ echo -1 > /proc/sys/kernel/sched_rr_timeslice_ms
$ cat /proc/sys/kernel/sched_rr_timeslice_ms
-1
Fix this by setting the variable that holds the sysctl file value to the
jiffies_to_msecs(RR_TIMESLICE) in case that <= 0 value was written.
Signed-off-by: Cyril Hrubis <chrubis@suse.cz>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Petr Vorel <pvorel@suse.cz>
Acked-by: Mel Gorman <mgorman@suse.de>
Tested-by: Petr Vorel <pvorel@suse.cz>
Link: https://lore.kernel.org/r/20230802151906.25258-3-chrubis@suse.cz
There is a 10% rounding error in the intial value of the
sysctl_sched_rr_timeslice with CONFIG_HZ_300=y.
This was found with LTP test sched_rr_get_interval01:
sched_rr_get_interval01.c:57: TPASS: sched_rr_get_interval() passed
sched_rr_get_interval01.c:64: TPASS: Time quantum 0s 99999990ns
sched_rr_get_interval01.c:72: TFAIL: /proc/sys/kernel/sched_rr_timeslice_ms != 100 got 90
sched_rr_get_interval01.c:57: TPASS: sched_rr_get_interval() passed
sched_rr_get_interval01.c:64: TPASS: Time quantum 0s 99999990ns
sched_rr_get_interval01.c:72: TFAIL: /proc/sys/kernel/sched_rr_timeslice_ms != 100 got 90
What this test does is to compare the return value from the
sched_rr_get_interval() and the sched_rr_timeslice_ms sysctl file and
fails if they do not match.
The problem it found is the intial sysctl file value which was computed as:
static int sysctl_sched_rr_timeslice = (MSEC_PER_SEC / HZ) * RR_TIMESLICE;
which works fine as long as MSEC_PER_SEC is multiple of HZ, however it
introduces 10% rounding error for CONFIG_HZ_300:
(MSEC_PER_SEC / HZ) * (100 * HZ / 1000)
(1000 / 300) * (100 * 300 / 1000)
3 * 30 = 90
This can be easily fixed by reversing the order of the multiplication
and division. After this fix we get:
(MSEC_PER_SEC * (100 * HZ / 1000)) / HZ
(1000 * (100 * 300 / 1000)) / 300
(1000 * 30) / 300 = 100
Fixes: 975e155ed873 ("sched/rt: Show the 'sched_rr_timeslice' SCHED_RR timeslice tuning knob in milliseconds")
Signed-off-by: Cyril Hrubis <chrubis@suse.cz>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Petr Vorel <pvorel@suse.cz>
Acked-by: Mel Gorman <mgorman@suse.de>
Tested-by: Petr Vorel <pvorel@suse.cz>
Link: https://lore.kernel.org/r/20230802151906.25258-2-chrubis@suse.cz
If an output buffer size exceeded U16_MAX, the min_t(u16, ...) cast in
copy_data() was causing writes to truncate. This manifested as output
bytes being skipped, seen as %NUL bytes in pstore dumps when the available
record size was larger than 65536. Fix the cast to no longer truncate
the calculation.
Cc: Petr Mladek <pmladek@suse.com>
Cc: Sergey Senozhatsky <senozhatsky@chromium.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: John Ogness <john.ogness@linutronix.de>
Reported-by: Vijay Balakrishna <vijayb@linux.microsoft.com>
Link: https://lore.kernel.org/lkml/d8bb1ec7-a4c5-43a2-9de0-9643a70b899f@linux.microsoft.com/
Fixes: b6cf8b3f3312 ("printk: add lockless ringbuffer")
Cc: stable@vger.kernel.org
Signed-off-by: Kees Cook <keescook@chromium.org>
Tested-by: Vijay Balakrishna <vijayb@linux.microsoft.com>
Tested-by: Guilherme G. Piccoli <gpiccoli@igalia.com> # Steam Deck
Reviewed-by: Tyler Hicks (Microsoft) <code@tyhicks.com>
Tested-by: Tyler Hicks (Microsoft) <code@tyhicks.com>
Reviewed-by: John Ogness <john.ogness@linutronix.de>
Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20230811054528.never.165-kees@kernel.org
- Make amd-pstate use device_attributes as expected by the CPU root
kobject (Thomas Weißschuh).
- Restore the previous behavior of resume_store() when hibernation is
not available which is to return the full number of bytes that were
to be written by user space (Vlastimil Babka).
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Merge tag 'pm-6.5-rc6' of git://git.kernel.org/pub/scm/linux/kernel/git/rafael/linux-pm
Pull power management fixes from Rafael Wysocki:
"These fix an amd-pstate cpufreq driver issues and recently introduced
hibernation-related breakage.
Specifics:
- Make amd-pstate use device_attributes as expected by the CPU root
kobject (Thomas Weißschuh)
- Restore the previous behavior of resume_store() when hibernation is
not available which is to return the full number of bytes that were
to be written by user space (Vlastimil Babka)"
* tag 'pm-6.5-rc6' of git://git.kernel.org/pub/scm/linux/kernel/git/rafael/linux-pm:
cpufreq: amd-pstate: fix global sysfs attribute type
PM: hibernate: fix resume_store() return value when hibernation not available
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Merge tag 'for-netdev' of https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next
Martin KaFai Lau says:
====================
pull-request: bpf-next 2023-08-09
We've added 19 non-merge commits during the last 6 day(s) which contain
a total of 25 files changed, 369 insertions(+), 141 deletions(-).
The main changes are:
1) Fix array-index-out-of-bounds access when detaching from an
already empty mprog entry from Daniel Borkmann.
2) Adjust bpf selftest because of a recent llvm change
related to the cpu-v4 ISA from Eduard Zingerman.
3) Add uprobe support for the bpf_get_func_ip helper from Jiri Olsa.
4) Fix a KASAN splat due to the kernel incorrectly accepted
an invalid program using the recent cpu-v4 instruction from
Yonghong Song.
* tag 'for-netdev' of https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next:
bpf: btf: Remove two unused function declarations
bpf: lru: Remove unused declaration bpf_lru_promote()
selftests/bpf: relax expected log messages to allow emitting BPF_ST
selftests/bpf: remove duplicated functions
bpf, docs: Fix small typo and define semantics of sign extension
selftests/bpf: Add bpf_get_func_ip test for uprobe inside function
selftests/bpf: Add bpf_get_func_ip tests for uprobe on function entry
bpf: Add support for bpf_get_func_ip helper for uprobe program
selftests/bpf: Add a movsx selftest for sign-extension of R10
bpf: Fix an incorrect verification success with movsx insn
bpf, docs: Formalize type notation and function semantics in ISA standard
bpf: change bpf_alu_sign_string and bpf_movsx_string to static
libbpf: Use local includes inside the library
bpf: fix bpf_dynptr_slice() to stop return an ERR_PTR.
bpf: fix inconsistent return types of bpf_xdp_copy_buf().
selftests/bpf: fix the incorrect verification of port numbers.
selftests/bpf: Add test for detachment on empty mprog entry
bpf: Fix mprog detachment for empty mprog entry
bpf: bpf_struct_ops: Remove unnecessary initial values of variables
====================
Link: https://lore.kernel.org/r/20230810055123.109578-1-martin.lau@linux.dev
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Pick up the EEVDF work into the main branch - it's looking good so far.
Conflicts:
kernel/sched/features.h
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Three LSMs register the implementations for the "capget" hook: AppArmor,
SELinux, and the normal capability code. Looking at the function
implementations we may observe that the first parameter "target" is not
changing.
Mark the first argument "target" of LSM hook security_capget() as
"const" since it will not be changing in the LSM hook.
cap_capget() LSM hook declaration exceeds the 80 characters per line
limit. Split the function declaration to multiple lines to decrease the
line length.
Signed-off-by: Khadija Kamran <kamrankhadijadj@gmail.com>
Acked-by: John Johansen <john.johansen@canonical.com>
[PM: align the cap_capget() declaration, spelling fixes]
Signed-off-by: Paul Moore <paul@paul-moore.com>
Tracefs or debugfs maybe cause hundreds to thousands of PATH records,
too many PATH records maybe cause soft lockup.
For example:
1. CONFIG_KASAN=y && CONFIG_PREEMPTION=n
2. auditctl -a exit,always -S open -k key
3. sysctl -w kernel.watchdog_thresh=5
4. mkdir /sys/kernel/debug/tracing/instances/test
There may be a soft lockup as follows:
watchdog: BUG: soft lockup - CPU#45 stuck for 7s! [mkdir:15498]
Kernel panic - not syncing: softlockup: hung tasks
Call trace:
dump_backtrace+0x0/0x30c
show_stack+0x20/0x30
dump_stack+0x11c/0x174
panic+0x27c/0x494
watchdog_timer_fn+0x2bc/0x390
__run_hrtimer+0x148/0x4fc
__hrtimer_run_queues+0x154/0x210
hrtimer_interrupt+0x2c4/0x760
arch_timer_handler_phys+0x48/0x60
handle_percpu_devid_irq+0xe0/0x340
__handle_domain_irq+0xbc/0x130
gic_handle_irq+0x78/0x460
el1_irq+0xb8/0x140
__audit_inode_child+0x240/0x7bc
tracefs_create_file+0x1b8/0x2a0
trace_create_file+0x18/0x50
event_create_dir+0x204/0x30c
__trace_add_new_event+0xac/0x100
event_trace_add_tracer+0xa0/0x130
trace_array_create_dir+0x60/0x140
trace_array_create+0x1e0/0x370
instance_mkdir+0x90/0xd0
tracefs_syscall_mkdir+0x68/0xa0
vfs_mkdir+0x21c/0x34c
do_mkdirat+0x1b4/0x1d4
__arm64_sys_mkdirat+0x4c/0x60
el0_svc_common.constprop.0+0xa8/0x240
do_el0_svc+0x8c/0xc0
el0_svc+0x20/0x30
el0_sync_handler+0xb0/0xb4
el0_sync+0x160/0x180
Therefore, we add cond_resched() to __audit_inode_child() to fix it.
Fixes: 5195d8e217a7 ("audit: dynamically allocate audit_names when not enough space is in the names array")
Signed-off-by: Gaosheng Cui <cuigaosheng1@huawei.com>
Signed-off-by: Paul Moore <paul@paul-moore.com>
Use a simple logical shift and increment to calculate the number of slots
taken by the DMA segment boundary.
At least GCC-13 is not able to optimize the expression, producing this
horrible assembly code on x86:
cmpq $-1, %rcx
je .L364
addq $2048, %rcx
shrq $11, %rcx
movq %rcx, %r13
.L331:
// rest of the function here...
// after function epilogue and return:
.L364:
movabsq $9007199254740992, %r13
jmp .L331
After the optimization, the code looks more reasonable:
shrq $11, %r11
leaq 1(%r11), %rbx
Signed-off-by: Petr Tesarik <petr.tesarik.ext@huawei.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Move the comment down in front of the loop that actually sets the list
member of struct io_tlb_slot to zero.
Fixes: 26a7e094783d ("swiotlb: refactor swiotlb_tbl_map_single")
Signed-off-by: Petr Tesarik <petr.tesarik.ext@huawei.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
While workqueue.default_affinity_scope is writable, it only affects
workqueues which are created afterwards and isn't very useful. Instead,
let's introduce explicit "default" scope and update the effective scope
dynamically when workqueue.default_affinity_scope is changed.
Signed-off-by: Tejun Heo <tj@kernel.org>
An unbound workqueue can be served by multiple worker_pools to improve
locality. The segmentation is achieved by grouping CPUs into pods. By
default, the cache boundaries according to cpus_share_cache() define the
CPUs are grouped. Let's a workqueue is allowed to run on all CPUs and the
system has two L3 caches. The workqueue would be mapped to two worker_pools
each serving one L3 cache domains.
While this improves locality, because the pod boundaries are strict, it
limits the total bandwidth a given issuer can consume. For example, let's
say there is a thread pinned to a CPU issuing enough work items to saturate
the whole machine. With the machine segmented into two pods, no matter how
many work items it issues, it can only use half of the CPUs on the system.
While this limitation has existed for a very long time, it wasn't very
pronounced because the affinity grouping used to be always by NUMA nodes.
With cache boundaries as the default and support for even finer grained
scopes (smt and cpu), it is now an a lot more pressing problem.
This patch implements non-strict affinity scope where the pod boundaries
aren't enforced strictly. Going back to the previous example, the workqueue
would still be mapped to two worker_pools; however, the affinity enforcement
would be soft. The workers in both pools would have their cpus_allowed set
to the whole machine thus allowing the scheduler to migrate them anywhere on
the machine. However, whenever an idle worker is woken up, the workqueue
code asks the scheduler to bring back the task within the pod if the worker
is outside. ie. work items start executing within its affinity scope but can
be migrated outside as the scheduler sees fit. This removes the hard cap on
utilization while maintaining the benefits of affinity scopes.
After the earlier ->__pod_cpumask changes, the implementation is pretty
simple. When non-strict which is the new default:
* pool_allowed_cpus() returns @pool->attrs->cpumask instead of
->__pod_cpumask so that the workers are allowed to run on any CPU that
the associated workqueues allow.
* If the idle worker task's ->wake_cpu is outside the pod, kick_pool() sets
the field to a CPU within the pod.
This would be the first use of task_struct->wake_cpu outside scheduler
proper, so it isn't clear whether this would be acceptable. However, other
methods of migrating tasks are significantly more expensive and are likely
prohibitively so if we want to do this on every work item. This needs
discussion with scheduler folks.
There is also a race window where setting ->wake_cpu wouldn't be effective
as the target task is still on CPU. However, the window is pretty small and
this being a best-effort optimization, it doesn't seem to warrant more
complexity at the moment.
While the non-strict cache affinity scopes seem to be the best option, the
performance picture interacts with the affinity scope and is a bit
complicated to fully discuss in this patch, so the behavior is made easily
selectable through wqattrs and sysfs and the next patch will add
documentation to discuss performance implications.
v2: pool->attrs->affn_strict is set to true for per-cpu worker_pools.
Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
workqueue_attrs has two uses:
* to specify the required unouned workqueue properties by users
* to match worker_pool's properties to workqueues by core code
For example, if the user wants to restrict a workqueue to run only CPUs 0
and 2, and the two CPUs are on different affinity scopes, the workqueue's
attrs->cpumask would contains CPUs 0 and 2, and the workqueue would be
associated with two worker_pools, one with attrs->cpumask containing just
CPU 0 and the other CPU 2.
Workqueue wants to support non-strict affinity scopes where work items are
started in their matching affinity scopes but the scheduler is free to
migrate them outside the starting scopes, which can enable utilizing the
whole machine while maintaining most of the locality benefits from affinity
scopes.
To enable that, worker_pools need to distinguish the strict affinity that it
has to follow (because that's the restriction coming from the user) and the
soft affinity that it wants to apply when dispatching work items. Note that
two worker_pools with different soft dispatching requirements have to be
separate; otherwise, for example, we'd be ping-ponging worker threads across
NUMA boundaries constantly.
This patch adds workqueue_attrs->__pod_cpumask. The new field is double
underscored as it's only used internally to distinguish worker_pools. A
worker_pool's ->cpumask is now always the same as the online subset of
allowed CPUs of the associated workqueues, and ->__pod_cpumask is the pod's
subset of that ->cpumask. Going back to the example above, both worker_pools
would have ->cpumask containing both CPUs 0 and 2 but one's ->__pod_cpumask
would contain 0 while the other's 2.
* pool_allowed_cpus() is added. It returns the worker_pool's strict cpumask
that the pool's workers must stay within. This is currently always
->__pod_cpumask as all boundaries are still strict.
* As a workqueue_attrs can now track both the associated workqueues' cpumask
and its per-pod subset, wq_calc_pod_cpumask() no longer needs an external
out-argument. Drop @cpumask and instead store the result in
->__pod_cpumask.
* The above also simplifies apply_wqattrs_prepare() as the same
workqueue_attrs can be used to create all pods associated with a
workqueue. tmp_attrs is dropped.
* wq_update_pod() is updated to use wqattrs_equal() to test whether a pwq
update is needed instead of only comparing ->cpumask so that
->__pod_cpumask is compared too. It can directly compare ->__pod_cpumaks
but the code is easier to understand and more robust this way.
The only user-visible behavior change is that two workqueues with different
cpumasks no longer can share worker_pools even when their pod subsets
coincide. Going back to the example, let's say there's another workqueue
with cpumask 0, 2, 3, where 2 and 3 are in the same pod. It would be mapped
to two worker_pools - one with CPU 0, the other with 2 and 3. The former has
the same cpumask as the first pod of the earlier example and would have
shared the same worker_pool but that's no longer the case after this patch.
The worker_pools would have the same ->__pod_cpumask but their ->cpumask's
wouldn't match.
While this is necessary to support non-strict affinity scopes, there can be
further optimizations to maintain sharing among strict affinity scopes.
However, non-strict affinity scopes are going to be preferable for most use
cases and we don't see very diverse mixture of unbound workqueue cpumasks
anyway, so the additional overhead doesn't seem to justify the extra
complexity.
v2: - wq_update_pod() was incorrectly comparing target_attrs->__pod_cpumask
to pool->attrs->cpumask instead of its ->__pod_cpumask. Fix it by
using wqattrs_equal() for comparison instead.
- Per-cpu worker pools weren't initializing ->__pod_cpumask which caused
a subtle problem later on. Set it to cpumask_of(cpu) like ->cpumask.
Signed-off-by: Tejun Heo <tj@kernel.org>
Checking need_more_worker() and calling wake_up_worker() is a repeated
pattern. Let's add kick_pool(), which checks need_more_worker() and
open-code wake_up_worker(), and replace wake_up_worker() uses. The following
conversions aren't one-to-one:
* __queue_work() was using __need_more_work() because it knows that
pool->worklist isn't empty. Switching to kick_pool() adds an extra
list_empty() test.
* create_worker() always needs to wake up the newly minted worker whether
there's more work to do or not to avoid triggering hung task check on the
new task. Keep the current wake_up_process() and still add kick_pool().
This may lead to an extra wakeup which isn't harmful.
* pwq_adjust_max_active() was explicitly checking whether it needs to wake
up a worker or not to avoid spurious wakeups. As kick_pool() only wakes up
a worker when necessary, this explicit check is no longer necessary and
dropped.
* unbind_workers() now calls kick_pool() instead of wake_up_worker() adding
a need_more_worker() test. This avoids spurious wakeups and shouldn't
break anything.
wake_up_worker() is dropped as kick_pool() replaces all its users. After
this patch, all paths that wakes up a non-rescuer worker to initiate work
item execution use kick_pool(). This will enable future changes to improve
locality.
Signed-off-by: Tejun Heo <tj@kernel.org>
The two work execution paths in worker_thread() and rescuer_thread() use
move_linked_works() to claim work items from @pool->worklist. Once claimed,
process_schedule_works() is called which invokes process_one_work() on each
work item. process_one_work() then uses find_worker_executing_work() to
detect and handle collisions - situations where the work item to be executed
is still running on another worker.
This works fine, but, to improve work execution locality, we want to
establish work to worker association earlier and know for sure that the
worker is going to excute the work once asssigned, which requires performing
collision handling earlier while trying to assign the work item to the
worker.
This patch introduces assign_work() which assigns a work item to a worker
using move_linked_works() and then performs collision handling. As collision
handling is handled earlier, process_one_work() no longer needs to worry
about them.
After the this patch, collision checks for linked work items are skipped,
which should be fine as they can't be queued multiple times concurrently.
For work items running from rescuers, the timing of collision handling may
change but the invariant that the work items go through collision handling
before starting execution does not.
This patch shouldn't cause noticeable behavior changes, especially given
that worker_thread() behavior remains the same.
Signed-off-by: Tejun Heo <tj@kernel.org>
Add three more affinity scopes - WQ_AFFN_CPU, SMT and CACHE - and make CACHE
the default. The code changes to actually add the additional scopes are
trivial.
Also add module parameter "workqueue.default_affinity_scope" to override the
default scope and "affinity_scope" sysfs file to configure it per workqueue.
wq_dump.py and documentations are updated accordingly.
This enables significant flexibility in configuring how unbound workqueues
behave. If affinity scope is set to "cpu", it'll behave close to a per-cpu
workqueue. On the other hand, "system" removes all locality boundaries.
Many modern machines have multiple L3 caches often while being mostly
uniform in terms of memory access. Thus, workqueue's previous behavior of
spreading work items in each NUMA node had negative performance implications
from unncessarily crossing L3 boundaries between issue and execution.
However, picking a finer grained affinity scope also has a downside in that
an issuer in one group can't utilize CPUs in other groups.
While dependent on the specifics of workload, there's usually a noticeable
penalty in crossing L3 boundaries, so let's default to CACHE. This issue
will be further addressed and documented with examples in future patches.
Signed-off-by: Tejun Heo <tj@kernel.org>
While wq_pod_type[] can now group CPUs in any aribitrary way, WQ_AFFN_NUM
init is hard coded into workqueue_init_topology(). This patch modularizes
the init path by introducing init_pod_type() which takes a callback to
determine whether two CPUs should share a pod as an argument.
init_pod_type() first scans the CPU combinations testing for sharing to
assign consecutive pod IDs and initialize pod_type->cpu_pod[]. Once
->cpu_pod[] is determined, ->pod_cpus[] and ->pod_node[] are initialized
accordingly. WQ_AFFN_NUMA is now initialized by calling init_pod_type() with
cpus_share_numa() which tests whether the CPU belongs to the same NUMA node.
This patch may change the pod ID assigned to each NUMA node but that
shouldn't cause any behavior changes as the NUMA node to use for allocations
are tracked separately in pod_type->pod_node[]. This makes adding new
affinty types pretty easy.
Signed-off-by: Tejun Heo <tj@kernel.org>
While renamed to pod, the code still assumes that the pods are defined by
NUMA boundaries. Let's generalize it:
* workqueue_attrs->affn_scope is added. Each enum represents the type of
boundaries that define the pods. There are currently two scopes -
WQ_AFFN_NUMA and WQ_AFFN_SYSTEM. The former is the same behavior as before
- one pod per NUMA node. The latter defines one global pod across the
whole system.
* struct wq_pod_type is added which describes how pods are configured for
each affnity scope. For each pod, it lists the member CPUs and the
preferred NUMA node for memory allocations. The reverse mapping from CPU
to pod is also available.
* wq_pod_enabled is dropped. Pod is now always enabled. The previously
disabled behavior is now implemented through WQ_AFFN_SYSTEM.
* get_unbound_pool() wants to determine the NUMA node to allocate memory
from for the new pool. The variables are renamed from node to pod but the
logic still assumes they're one and the same. Clearly distinguish them -
walk the WQ_AFFN_NUMA pods to find the matching pod and then use the pod's
NUMA node.
* wq_calc_pod_cpumask() was taking @pod but assumed that it was the NUMA
node. Take @cpu instead and determine the cpumask to use from the pod_type
matching @attrs.
* apply_wqattrs_prepare() is update to return ERR_PTR() on error instead of
NULL so that it can indicate -EINVAL on invalid affinity scopes.
This patch allows CPUs to be grouped into pods however desired per type.
While this patch causes some internal behavior changes, nothing material
should change for workqueue users.
v2: Trigger WARN_ON_ONCE() in wqattrs_pod_type() if affn_scope is
WQ_AFFN_NR_TYPES which indicates that the function is called with a
worker_pool's attrs instead of a workqueue's.
Signed-off-by: Tejun Heo <tj@kernel.org>
workqueue_attrs can be used for both workqueues and worker_pools. However,
some fields, currently only ->ordered, only apply to workqueues and should
be cleared to the default / invalid values.
Currently, an unbound workqueue explicitly clears attrs->ordered in
get_unbound_pool() after copying the source workqueue attrs, while per-cpu
workqueues rely on the fact that zeroing on allocation gives us the desired
default value for pool->attrs->ordered.
This is fragile. Let's add wqattrs_clear_for_pool() which clears
attrs->ordered and is called from both init_worker_pool() and
get_unbound_pool(). This will ease adding more workqueue-only attrs fields.
In get_unbound_pool(), pool->node initialization is moved upwards for
readability. This shouldn't cause any behavior changes.
Signed-off-by: Tejun Heo <tj@kernel.org>
For an unbound pool, multiple cpumasks are involved.
U: The user-specified cpumask (may be filtered with cpu_possible_mask).
A: The actual cpumask filtered by wq_unbound_cpumask. If the filtering
leaves no CPU, wq_unbound_cpumask is used.
P: Per-pod subsets of #A.
wq->attrs stores #U, wq->dfl_pwq->pool->attrs->cpumask #A, and
wq->cpu_pwq[CPU]->pool->attrs->cpumask #P.
wq_update_pod() is called to update per-pod pwq's during CPU hotplug. To
calculate the new #P for each workqueue, it needs to call
wq_calc_pod_cpumask() with @attrs that contains #A. Currently,
wq_update_pod() achieves this by calling wq_calc_pod_cpumask() with
wq->dfl_pwq->pool->attrs.
This is rather fragile because we're calling wq_calc_pod_cpumask() with
@attrs of a worker_pool rather than the workqueue's actual attrs when what
we want to calculate is the workqueue's cpumask on the pod. While this works
fine currently, future changes will add fields which are used differently
between workqueues and worker_pools and this subtlety will bite us.
This patch factors out #U -> #A calculation from apply_wqattrs_prepare()
into wqattrs_actualize_cpumask and updates wq_update_pod() to copy
wq->unbound_attrs and use the new helper to obtain #A freshly instead of
abusing wq->dfl_pwq->pool_attrs.
This shouldn't cause any behavior changes in the current code.
Signed-off-by: Tejun Heo <tj@kernel.org>
Reported-by: K Prateek Nayak <kprateek.nayak@amd.com>
Reference: http://lkml.kernel.org/r/30625cdd-4d61-594b-8db9-6816b017dde3@amd.com
During boot, to initialize unbound CPU pods, wq_pod_init() was called from
workqueue_init(). This is early enough for NUMA nodes to be set up but
before SMP is brought up and CPU topology information is populated.
Workqueue is in the process of improving CPU locality for unbound workqueues
and will need access to topology information during pod init. This adds a
new init function workqueue_init_topology() which is called after CPU
topology information is available and replaces wq_pod_init().
As unbound CPU pods are now initialized after workqueues are activated, we
need to revisit the workqueues to apply the pod configuration. Workqueues
which are created before workqueue_init_topology() are set up so that they
always use the default worker pool. After pods are set up in
workqueue_init_topology(), wq_update_pod() is called on all existing
workqueues to update the pool associations accordingly.
Note that wq_update_pod_attrs_buf allocation is moved to
workqueue_init_early(). This isn't necessary right now but enables further
generalization of pod handling in the future.
This patch changes the initialization sequence but the end result should be
the same.
Signed-off-by: Tejun Heo <tj@kernel.org>
wq_pod_init() is called from workqueue_init() and responsible for
initializing unbound CPU pods according to NUMA node. Workqueue is in the
process of improving affinity awareness and wants to use other topology
information to initialize unbound CPU pods; however, unlike NUMA nodes,
other topology information isn't yet available in workqueue_init().
The next patch will introduce a later stage init function for workqueue
which will be responsible for initializing unbound CPU pods. Relocate
wq_pod_init() below workqueue_init() where the new init function is going to
be located so that the diff can show the content differences.
Just a relocation. No functional changes.
Signed-off-by: Tejun Heo <tj@kernel.org>
Workqueue is in the process of improving CPU affinity awareness. It will
become more flexible and won't be tied to NUMA node boundaries. This patch
renames all NUMA related names in workqueue.c to use "pod" instead.
While "pod" isn't a very common term, it short and captures the grouping of
CPUs well enough. These names are only going to be used within workqueue
implementation proper, so the specific naming doesn't matter that much.
* wq_numa_possible_cpumask -> wq_pod_cpus
* wq_numa_enabled -> wq_pod_enabled
* wq_update_unbound_numa_attrs_buf -> wq_update_pod_attrs_buf
* workqueue_select_cpu_near -> select_numa_node_cpu
This rename is different from others. The function is only used by
queue_work_node() and specifically tries to find a CPU in the specified
NUMA node. As workqueue affinity will become more flexible and untied from
NUMA, this function's name should specifically describe that it's for
NUMA.
* wq_calc_node_cpumask -> wq_calc_pod_cpumask
* wq_update_unbound_numa -> wq_update_pod
* wq_numa_init -> wq_pod_init
* node -> pod in local variables
Only renames. No functional changes.
Signed-off-by: Tejun Heo <tj@kernel.org>
With the recent removal of NUMA related module param and sysfs knob,
workqueue_attrs->no_numa is now only used to implement ordered workqueues.
Let's rename the field so that it's less confusing especially with the
planned CPU affinity awareness improvements.
Just a rename. No functional changes.
Signed-off-by: Tejun Heo <tj@kernel.org>
A pwq (pool_workqueue) represents an association between a workqueue and a
worker_pool. When a work item is queued, the workqueue selects the pwq to
use, which in turn determines the pool, and queues the work item to the pool
through the pwq. pwq is also what implements the maximum concurrency limit -
@max_active.
As a per-cpu workqueue should be assocaited with a different worker_pool on
each CPU, it always had per-cpu pwq's that are accessed through wq->cpu_pwq.
However, unbound workqueues were sharing a pwq within each NUMA node by
default. The sharing has several downsides:
* Because @max_active is per-pwq, the meaning of @max_active changes
depending on the machine configuration and whether workqueue NUMA locality
support is enabled.
* Makes per-cpu and unbound code deviate.
* Gets in the way of making workqueue CPU locality awareness more flexible.
This patch makes unbound workqueues use per-cpu pwq's the same way per-cpu
workqueues do by making the following changes:
* wq->numa_pwq_tbl[] is removed and unbound workqueues now use wq->cpu_pwq
just like per-cpu workqueues. wq->cpu_pwq is now RCU protected for unbound
workqueues.
* numa_pwq_tbl_install() is renamed to install_unbound_pwq() and installs
the specified pwq to the target CPU's wq->cpu_pwq.
* apply_wqattrs_prepare() now always allocates a separate pwq for each CPU
unless the workqueue is ordered. If ordered, all CPUs use wq->dfl_pwq.
This makes the return value of wq_calc_node_cpumask() unnecessary. It now
returns void.
* @max_active now means the same thing for both per-cpu and unbound
workqueues. WQ_UNBOUND_MAX_ACTIVE now equals WQ_MAX_ACTIVE and
documentation is updated accordingly. WQ_UNBOUND_MAX_ACTIVE is no longer
used in workqueue implementation and will be removed later.
* All unbound pwq operations which used to be per-numa-node are now per-cpu.
For most unbound workqueue users, this shouldn't cause noticeable changes.
Work item issue and completion will be a small bit faster, flush_workqueue()
would become a bit more expensive, and the total concurrency limit would
likely become higher. All @max_active==1 use cases are currently being
audited for conversion into alloc_ordered_workqueue() and they shouldn't be
affected once the audit and conversion is complete.
One area where the behavior change may be more noticeable is
workqueue_congested() as the reported congestion state is now per CPU
instead of NUMA node. There are only two users of this interface -
drivers/infiniband/hw/hfi1 and net/smc. Maintainers of both subsystems are
cc'd. Inputs on the behavior change would be very much appreciated.
Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Dennis Dalessandro <dennis.dalessandro@cornelisnetworks.com>
Cc: Jason Gunthorpe <jgg@ziepe.ca>
Cc: Leon Romanovsky <leon@kernel.org>
Cc: Karsten Graul <kgraul@linux.ibm.com>
Cc: Wenjia Zhang <wenjia@linux.ibm.com>
Cc: Jan Karcher <jaka@linux.ibm.com>
When a CPU went online or offline, wq_update_unbound_numa() was called only
on the CPU which was going up or down. This works fine because all CPUs on
the same NUMA node share the same pool_workqueue slot - one CPU updating it
updates it for everyone in the node.
However, future changes will make each CPU use a separate pool_workqueue
even when they're sharing the same worker_pool, which requires updating
pool_workqueue's for all CPUs which may be sharing the same pool_workqueue
on hotplug.
To accommodate the planned changes, this patch updates
workqueue_on/offline_cpu() so that they call wq_update_unbound_numa() for
all CPUs sharing the same NUMA node as the CPU going up or down. In the
current code, the second+ calls would be noops and there shouldn't be any
behavior changes.
* As wq_update_unbound_numa() is now called on multiple CPUs per each
hotplug event, @cpu is renamed to @hotplug_cpu and another @cpu argument
is added. The former indicates the CPU being hot[un]plugged and the latter
the CPU whose pool_workqueue is being updated.
* In wq_update_unbound_numa(), cpu_off is renamed to off_cpu for consistency
with the new @hotplug_cpu.
Signed-off-by: Tejun Heo <tj@kernel.org>
Currently, all per-cpu pwq's (pool_workqueue's) are allocated directly
through a per-cpu allocation and thus, unlike unbound workqueues, not
reference counted. This difference in lifetime management between the two
types is a bit confusing.
Unbound workqueues are currently accessed through wq->numa_pwq_tbl[] which
isn't suitiable for the planned CPU locality related improvements. The plan
is to unify pwq handling across per-cpu and unbound workqueues so that
they're always accessed through wq->cpu_pwq.
In preparation, this patch makes per-cpu pwq's to be allocated, reference
counted and released the same way as unbound pwq's. wq->cpu_pwq now holds
pointers to pwq's instead of containing them directly.
pwq_unbound_release_workfn() is renamed to pwq_release_workfn() as it's now
also used for per-cpu work items.
Signed-off-by: Tejun Heo <tj@kernel.org>
pool_workqueue release path is currently bounced to system_wq; however, this
is a bit tricky because this bouncing occurs while holding a pool lock and
thus has risk of causing a A-A deadlock. This is currently addressed by the
fact that only unbound workqueues use this bouncing path and system_wq is a
per-cpu workqueue.
While this works, it's brittle and requires a work-around like setting the
lockdep subclass for the lock of unbound pools. Besides, future changes will
use the bouncing path for per-cpu workqueues too making the current approach
unusable.
Let's just use a dedicated kthread_worker to untangle the dependency. This
is just one more kthread for all workqueues and makes the pwq release logic
simpler and more robust.
Signed-off-by: Tejun Heo <tj@kernel.org>
Unbound workqueue CPU affinity is going to receive an overhaul and the NUMA
specific knobs won't make sense anymore. Remove them. Also, the pool_ids
knob was used for debugging and not really meaningful given that there is no
visibility into the pools associated with those IDs. Remove it too. A future
patch will improve overall visibility.
Signed-off-by: Tejun Heo <tj@kernel.org>
Collect first_idle_worker(), worker_enter/leave_idle(),
find_worker_executing_work(), move_linked_works() and wake_up_worker() into
one place. These functions will later be used to implement higher level
worker management logic.
No functional changes.
Signed-off-by: Tejun Heo <tj@kernel.org>
wq->cpu_pwqs is a percpu variable carraying one pointer to a pool_workqueue.
The field name being plural is unusual and confusing. Rename it to singular.
This patch doesn't cause any functional changes.
Signed-off-by: Tejun Heo <tj@kernel.org>
insert_work() always tried to wake up a worker; however, the only time it
needs to try to wake up a worker is when a new active work item is queued.
When a work item goes on the inactive list or queueing a flush work item,
there's no reason to try to wake up a worker.
This patch moves the worker wakeup logic out of insert_work() and places it
in the active new work item queueing path in __queue_work().
While at it:
* __queue_work() is dereferencing pwq->pool repeatedly. Add local variable
pool.
* Every caller of insert_work() calls debug_work_activate(). Consolidate the
invocations into insert_work().
* In __queue_work() pool->watchdog_ts update is relocated slightly. This is
to better accommodate future changes.
This makes wakeups more precise and will help the planned change to assign
work items to workers before waking them up. No behavior changes intended.
v2: WARN_ON_ONCE(pool != last_pool) added in __queue_work() to clarify as
suggested by Lai.
Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Lai Jiangshan <jiangshanlai@gmail.com>
* Drop the trivial optimization in worker_thread() where it bypasses calling
process_scheduled_works() if the first work item isn't linked. This is a
mostly pointless micro optimization and gets in the way of improving the
work processing path.
* Consolidate pool->watchdog_ts updates in the two callers into
process_scheduled_works().
Signed-off-by: Tejun Heo <tj@kernel.org>
worker->flags used to be accessed from scheduler hooks without grabbing
pool->lock for concurrency management. This is no longer true since
6d25be5782e4 ("sched/core, workqueues: Distangle worker accounting from rq
lock"). Also, it's unclear why worker_pool->flags was using the "X" rule.
All relevant users are accessing it under the pool lock.
Let's drop the special "X" rule and use the "L" rule for these flag fields
instead. While at it, replace the CONTEXT comment with
lockdep_assert_held().
This allows worker_set/clr_flags() to be used from context which isn't the
worker itself. This will be used later to implement assinging work items to
workers before waking them up so that workqueue can have better control over
which worker executes which work item on which CPU.
The only actual changes are sanity checks. There shouldn't be any visible
behavior changes.
Signed-off-by: Tejun Heo <tj@kernel.org>
Unbound workqueue execution locality improvement patchset is about to
applied which will cause merge conflicts with changes in for-6.5-fixes.
Let's avoid future merge conflict by pulling in for-6.5-fixes.
Signed-off-by: Tejun Heo <tj@kernel.org>
Adding support for bpf_get_func_ip helper for uprobe program to return
probed address for both uprobe and return uprobe.
We discussed this in [1] and agreed that uprobe can have special use
of bpf_get_func_ip helper that differs from kprobe.
The kprobe bpf_get_func_ip returns:
- address of the function if probe is attach on function entry
for both kprobe and return kprobe
- 0 if the probe is not attach on function entry
The uprobe bpf_get_func_ip returns:
- address of the probe for both uprobe and return uprobe
The reason for this semantic change is that kernel can't really tell
if the probe user space address is function entry.
The uprobe program is actually kprobe type program attached as uprobe.
One of the consequences of this design is that uprobes do not have its
own set of helpers, but share them with kprobes.
As we need different functionality for bpf_get_func_ip helper for uprobe,
I'm adding the bool value to the bpf_trace_run_ctx, so the helper can
detect that it's executed in uprobe context and call specific code.
The is_uprobe bool is set as true in bpf_prog_run_array_sleepable, which
is currently used only for executing bpf programs in uprobe.
Renaming bpf_prog_run_array_sleepable to bpf_prog_run_array_uprobe
to address that it's only used for uprobes and that it sets the
run_ctx.is_uprobe as suggested by Yafang Shao.
Suggested-by: Andrii Nakryiko <andrii@kernel.org>
Tested-by: Alan Maguire <alan.maguire@oracle.com>
[1] https://lore.kernel.org/bpf/CAEf4BzZ=xLVkG5eurEuvLU79wAMtwho7ReR+XJAgwhFF4M-7Cg@mail.gmail.com/
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Tested-by: Viktor Malik <vmalik@redhat.com>
Acked-by: Yonghong Song <yonghong.song@linux.dev>
Link: https://lore.kernel.org/r/20230807085956.2344866-2-jolsa@kernel.org
Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>
