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This release cycle is rather small. Just a few fixes to tracing.

Browse Source 
The big change is the addition of the hwlat tracer. It not only detects
 SMIs, but also other latency that's caused by the hardware. I have detected
 some latency from large boxes having bus contention.
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Merge tag 'trace-v4.9' of git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace

Pull tracing updates from Steven Rostedt:
 "This release cycle is rather small.  Just a few fixes to tracing.

  The big change is the addition of the hwlat tracer. It not only
  detects SMIs, but also other latency that's caused by the hardware. I
  have detected some latency from large boxes having bus contention"

* tag 'trace-v4.9' of git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace:
  tracing: Call traceoff trigger after event is recorded
  ftrace/scripts: Add helper script to bisect function tracing problem functions
  tracing: Have max_latency be defined for HWLAT_TRACER as well
  tracing: Add NMI tracing in hwlat detector
  tracing: Have hwlat trace migrate across tracing_cpumask CPUs
  tracing: Add documentation for hwlat_detector tracer
  tracing: Added hardware latency tracer
  ftrace: Access ret_stack->subtime only in the function profiler
  function_graph: Handle TRACE_BPUTS in print_graph_comment
  tracing/uprobe: Drop isdigit() check in create_trace_uprobe
This commit is contained in:
Linus Torvalds 2016-10-06 11:48:41 -07:00
commit 95107b30be
17 changed files with 1013 additions and 20 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

10
Documentation/trace/ftrace.txt
View File

@ -858,11 +858,11 @@ x494] <- /root/a.out[+0x4a8] <- /lib/libc-2.7.so[+0x1e1a6]
When enabled, it will account time the task has been
scheduled out as part of the function call.
graph-time - When running function graph tracer, to include the
time to call nested functions. When this is not set,
the time reported for the function will only include
the time the function itself executed for, not the time
for functions that it called.
graph-time - When running function profiler with function graph tracer,
to include the time to call nested functions. When this is
not set, the time reported for the function will only
include the time the function itself executed for, not the
time for functions that it called.
record-cmd - When any event or tracer is enabled, a hook is enabled
in the sched_switch trace point to fill comm cache

79
Documentation/trace/hwlat_detector.txt Normal file
View File

@ -0,0 +1,79 @@
Introduction:
-------------
The tracer hwlat_detector is a special purpose tracer that is used to
detect large system latencies induced by the behavior of certain underlying
hardware or firmware, independent of Linux itself. The code was developed
originally to detect SMIs (System Management Interrupts) on x86 systems,
however there is nothing x86 specific about this patchset. It was
originally written for use by the "RT" patch since the Real Time
kernel is highly latency sensitive.
SMIs are not serviced by the Linux kernel, which means that it does not
even know that they are occuring. SMIs are instead set up by BIOS code
and are serviced by BIOS code, usually for "critical" events such as
management of thermal sensors and fans. Sometimes though, SMIs are used for
other tasks and those tasks can spend an inordinate amount of time in the
handler (sometimes measured in milliseconds). Obviously this is a problem if
you are trying to keep event service latencies down in the microsecond range.
The hardware latency detector works by hogging one of the cpus for configurable
amounts of time (with interrupts disabled), polling the CPU Time Stamp Counter
for some period, then looking for gaps in the TSC data. Any gap indicates a
time when the polling was interrupted and since the interrupts are disabled,
the only thing that could do that would be an SMI or other hardware hiccup
(or an NMI, but those can be tracked).
Note that the hwlat detector should *NEVER* be used in a production environment.
It is intended to be run manually to determine if the hardware platform has a
problem with long system firmware service routines.
Usage:
------
Write the ASCII text "hwlat" into the current_tracer file of the tracing system
(mounted at /sys/kernel/tracing or /sys/kernel/tracing). It is possible to
redefine the threshold in microseconds (us) above which latency spikes will
be taken into account.
Example:
# echo hwlat > /sys/kernel/tracing/current_tracer
# echo 100 > /sys/kernel/tracing/tracing_thresh
The /sys/kernel/tracing/hwlat_detector interface contains the following files:
width - time period to sample with CPUs held (usecs)
must be less than the total window size (enforced)
window - total period of sampling, width being inside (usecs)
By default the width is set to 500,000 and window to 1,000,000, meaning that
for every 1,000,000 usecs (1s) the hwlat detector will spin for 500,000 usecs
(0.5s). If tracing_thresh contains zero when hwlat tracer is enabled, it will
change to a default of 10 usecs. If any latencies that exceed the threshold is
observed then the data will be written to the tracing ring buffer.
The minimum sleep time between periods is 1 millisecond. Even if width
is less than 1 millisecond apart from window, to allow the system to not
be totally starved.
If tracing_thresh was zero when hwlat detector was started, it will be set
back to zero if another tracer is loaded. Note, the last value in
tracing_thresh that hwlat detector had will be saved and this value will
be restored in tracing_thresh if it is still zero when hwlat detector is
started again.
The following tracing directory files are used by the hwlat_detector:
in /sys/kernel/tracing:
tracing_threshold - minimum latency value to be considered (usecs)
tracing_max_latency - maximum hardware latency actually observed (usecs)
tracing_cpumask - the CPUs to move the hwlat thread across
hwlat_detector/width - specified amount of time to spin within window (usecs)
hwlat_detector/window - amount of time between (width) runs (usecs)
The hwlat detector's kernel thread will migrate across each CPU specified in
tracing_cpumask between each window. To limit the migration, either modify
tracing_cpumask, or modify the hwlat kernel thread (named [hwlatd]) CPU
affinity directly, and the migration will stop.

4
arch/sh/kernel/ftrace.c
View File

@ -139,7 +139,7 @@ static void ftrace_mod_code(void)
clear_mod_flag();
}
void ftrace_nmi_enter(void)
void arch_ftrace_nmi_enter(void)
{
if (atomic_inc_return(&nmi_running) & MOD_CODE_WRITE_FLAG) {
smp_rmb();
@ -150,7 +150,7 @@ void ftrace_nmi_enter(void)
smp_mb();
}
void ftrace_nmi_exit(void)
void arch_ftrace_nmi_exit(void)
{
/* Finish all executions before clearing nmi_running */
smp_mb();

2
include/linux/ftrace.h
View File

@ -794,7 +794,9 @@ struct ftrace_ret_stack {
unsigned long ret;
unsigned long func;
unsigned long long calltime;
#ifdef CONFIG_FUNCTION_PROFILER
unsigned long long subtime;
#endif
#ifdef HAVE_FUNCTION_GRAPH_FP_TEST
unsigned long fp;
#endif

31
include/linux/ftrace_irq.h
View File

@ -3,11 +3,34 @@
#ifdef CONFIG_FTRACE_NMI_ENTER
extern void ftrace_nmi_enter(void);
extern void ftrace_nmi_exit(void);
extern void arch_ftrace_nmi_enter(void);
extern void arch_ftrace_nmi_exit(void);
#else
static inline void ftrace_nmi_enter(void) { }
static inline void ftrace_nmi_exit(void) { }
static inline void arch_ftrace_nmi_enter(void) { }
static inline void arch_ftrace_nmi_exit(void) { }
#endif
#ifdef CONFIG_HWLAT_TRACER
extern bool trace_hwlat_callback_enabled;
extern void trace_hwlat_callback(bool enter);
#endif
static inline void ftrace_nmi_enter(void)
{
#ifdef CONFIG_HWLAT_TRACER
if (trace_hwlat_callback_enabled)
trace_hwlat_callback(true);
#endif
arch_ftrace_nmi_enter();
}
static inline void ftrace_nmi_exit(void)
{
arch_ftrace_nmi_exit();
#ifdef CONFIG_HWLAT_TRACER
if (trace_hwlat_callback_enabled)
trace_hwlat_callback(false);
#endif
}
#endif /* _LINUX_FTRACE_IRQ_H */

35
kernel/trace/Kconfig
View File

@ -216,6 +216,41 @@ config SCHED_TRACER
This tracer tracks the latency of the highest priority task
to be scheduled in, starting from the point it has woken up.
config HWLAT_TRACER
bool "Tracer to detect hardware latencies (like SMIs)"
select GENERIC_TRACER
help
This tracer, when enabled will create one or more kernel threads,
depening on what the cpumask file is set to, which each thread
spinning in a loop looking for interruptions caused by
something other than the kernel. For example, if a
System Management Interrupt (SMI) takes a noticeable amount of
time, this tracer will detect it. This is useful for testing
if a system is reliable for Real Time tasks.
Some files are created in the tracing directory when this
is enabled:
hwlat_detector/width - time in usecs for how long to spin for
hwlat_detector/window - time in usecs between the start of each
iteration
A kernel thread is created that will spin with interrupts disabled
for "width" microseconds in every "widow" cycle. It will not spin
for "window - width" microseconds, where the system can
continue to operate.
The output will appear in the trace and trace_pipe files.
When the tracer is not running, it has no affect on the system,
but when it is running, it can cause the system to be
periodically non responsive. Do not run this tracer on a
production system.
To enable this tracer, echo in "hwlat" into the current_tracer
file. Every time a latency is greater than tracing_thresh, it will
be recorded into the ring buffer.
config ENABLE_DEFAULT_TRACERS
bool "Trace process context switches and events"
depends on !GENERIC_TRACER

1
kernel/trace/Makefile
View File

@ -41,6 +41,7 @@ obj-$(CONFIG_FUNCTION_TRACER) += trace_functions.o
obj-$(CONFIG_IRQSOFF_TRACER) += trace_irqsoff.o
obj-$(CONFIG_PREEMPT_TRACER) += trace_irqsoff.o
obj-$(CONFIG_SCHED_TRACER) += trace_sched_wakeup.o
obj-$(CONFIG_HWLAT_TRACER) += trace_hwlat.o
obj-$(CONFIG_NOP_TRACER) += trace_nop.o
obj-$(CONFIG_STACK_TRACER) += trace_stack.o
obj-$(CONFIG_MMIOTRACE) += trace_mmiotrace.o

6
kernel/trace/ftrace.c
View File

@ -872,7 +872,13 @@ function_profile_call(unsigned long ip, unsigned long parent_ip,
#ifdef CONFIG_FUNCTION_GRAPH_TRACER
static int profile_graph_entry(struct ftrace_graph_ent *trace)
{
int index = trace->depth;
function_profile_call(trace->func, 0, NULL, NULL);
if (index >= 0 && index < FTRACE_RETFUNC_DEPTH)
current->ret_stack[index].subtime = 0;
return 1;
}

8
kernel/trace/trace.c
View File

@ -1047,7 +1047,7 @@ void disable_trace_on_warning(void)
*
* Shows real state of the ring buffer if it is enabled or not.
*/
static int tracer_tracing_is_on(struct trace_array *tr)
int tracer_tracing_is_on(struct trace_array *tr)
{
if (tr->trace_buffer.buffer)
return ring_buffer_record_is_on(tr->trace_buffer.buffer);
@ -4969,7 +4969,7 @@ out:
return ret;
}
#ifdef CONFIG_TRACER_MAX_TRACE
#if defined(CONFIG_TRACER_MAX_TRACE) || defined(CONFIG_HWLAT_TRACER)
static ssize_t
tracing_max_lat_read(struct file *filp, char __user *ubuf,
@ -5892,7 +5892,7 @@ static const struct file_operations tracing_thresh_fops = {
.llseek = generic_file_llseek,
};
#ifdef CONFIG_TRACER_MAX_TRACE
#if defined(CONFIG_TRACER_MAX_TRACE) || defined(CONFIG_HWLAT_TRACER)
static const struct file_operations tracing_max_lat_fops = {
.open = tracing_open_generic,
.read = tracing_max_lat_read,
@ -7222,7 +7222,7 @@ init_tracer_tracefs(struct trace_array *tr, struct dentry *d_tracer)
create_trace_options_dir(tr);
#ifdef CONFIG_TRACER_MAX_TRACE
#if defined(CONFIG_TRACER_MAX_TRACE) || defined(CONFIG_HWLAT_TRACER)
trace_create_file("tracing_max_latency", 0644, d_tracer,
&tr->max_latency, &tracing_max_lat_fops);
#endif

5
kernel/trace/trace.h
View File

@ -38,6 +38,7 @@ enum trace_type {
TRACE_USER_STACK,
TRACE_BLK,
TRACE_BPUTS,
TRACE_HWLAT,
__TRACE_LAST_TYPE,
};
@ -213,6 +214,8 @@ struct trace_array {
*/
struct trace_buffer max_buffer;
bool allocated_snapshot;
#endif
#if defined(CONFIG_TRACER_MAX_TRACE) || defined(CONFIG_HWLAT_TRACER)
unsigned long max_latency;
#endif
struct trace_pid_list __rcu *filtered_pids;
@ -326,6 +329,7 @@ extern void __ftrace_bad_type(void);
IF_ASSIGN(var, ent, struct print_entry, TRACE_PRINT); \
IF_ASSIGN(var, ent, struct bprint_entry, TRACE_BPRINT); \
IF_ASSIGN(var, ent, struct bputs_entry, TRACE_BPUTS); \
IF_ASSIGN(var, ent, struct hwlat_entry, TRACE_HWLAT); \
IF_ASSIGN(var, ent, struct trace_mmiotrace_rw, \
TRACE_MMIO_RW); \
IF_ASSIGN(var, ent, struct trace_mmiotrace_map, \
@ -571,6 +575,7 @@ void tracing_reset_current(int cpu);
void tracing_reset_all_online_cpus(void);
int tracing_open_generic(struct inode *inode, struct file *filp);
bool tracing_is_disabled(void);
int tracer_tracing_is_on(struct trace_array *tr);
struct dentry *trace_create_file(const char *name,
umode_t mode,
struct dentry *parent,

27
kernel/trace/trace_entries.h
View File

@ -322,3 +322,30 @@ FTRACE_ENTRY(branch, trace_branch,
FILTER_OTHER
);
FTRACE_ENTRY(hwlat, hwlat_entry,
TRACE_HWLAT,
F_STRUCT(
__field( u64, duration )
__field( u64, outer_duration )
__field( u64, nmi_total_ts )
__field_struct( struct timespec, timestamp )
__field_desc( long, timestamp, tv_sec )
__field_desc( long, timestamp, tv_nsec )
__field( unsigned int, nmi_count )
__field( unsigned int, seqnum )
),
F_printk("cnt:%u\tts:%010lu.%010lu\tinner:%llu\touter:%llunmi-ts:%llu\tnmi-count:%u\n",
__entry->seqnum,
__entry->tv_sec,
__entry->tv_nsec,
__entry->duration,
__entry->outer_duration,
__entry->nmi_total_ts,
__entry->nmi_count),
FILTER_OTHER
);

1
kernel/trace/trace_events_trigger.c
View File

@ -1028,6 +1028,7 @@ static struct event_command trigger_traceon_cmd = {
static struct event_command trigger_traceoff_cmd = {
.name = "traceoff",
.trigger_type = ETT_TRACE_ONOFF,
.flags = EVENT_CMD_FL_POST_TRIGGER,
.func = event_trigger_callback,
.reg = register_trigger,
.unreg = unregister_trigger,

6
kernel/trace/trace_functions_graph.c
View File

@ -170,7 +170,6 @@ ftrace_push_return_trace(unsigned long ret, unsigned long func, int *depth,
current->ret_stack[index].ret = ret;
current->ret_stack[index].func = func;
current->ret_stack[index].calltime = calltime;
current->ret_stack[index].subtime = 0;
#ifdef HAVE_FUNCTION_GRAPH_FP_TEST
current->ret_stack[index].fp = frame_pointer;
#endif
@ -1183,6 +1182,11 @@ print_graph_comment(struct trace_seq *s, struct trace_entry *ent,
trace_seq_puts(s, "/* ");
switch (iter->ent->type) {
case TRACE_BPUTS:
ret = trace_print_bputs_msg_only(iter);
if (ret != TRACE_TYPE_HANDLED)
return ret;
break;
case TRACE_BPRINT:
ret = trace_print_bprintk_msg_only(iter);
if (ret != TRACE_TYPE_HANDLED)

633
kernel/trace/trace_hwlat.c Normal file
View File

@ -0,0 +1,633 @@
/*
* trace_hwlatdetect.c - A simple Hardware Latency detector.
*
* Use this tracer to detect large system latencies induced by the behavior of
* certain underlying system hardware or firmware, independent of Linux itself.
* The code was developed originally to detect the presence of SMIs on Intel
* and AMD systems, although there is no dependency upon x86 herein.
*
* The classical example usage of this tracer is in detecting the presence of
* SMIs or System Management Interrupts on Intel and AMD systems. An SMI is a
* somewhat special form of hardware interrupt spawned from earlier CPU debug
* modes in which the (BIOS/EFI/etc.) firmware arranges for the South Bridge
* LPC (or other device) to generate a special interrupt under certain
* circumstances, for example, upon expiration of a special SMI timer device,
* due to certain external thermal readings, on certain I/O address accesses,
* and other situations. An SMI hits a special CPU pin, triggers a special
* SMI mode (complete with special memory map), and the OS is unaware.
*
* Although certain hardware-inducing latencies are necessary (for example,
* a modern system often requires an SMI handler for correct thermal control
* and remote management) they can wreak havoc upon any OS-level performance
* guarantees toward low-latency, especially when the OS is not even made
* aware of the presence of these interrupts. For this reason, we need a
* somewhat brute force mechanism to detect these interrupts. In this case,
* we do it by hogging all of the CPU(s) for configurable timer intervals,
* sampling the built-in CPU timer, looking for discontiguous readings.
*
* WARNING: This implementation necessarily introduces latencies. Therefore,
* you should NEVER use this tracer while running in a production
* environment requiring any kind of low-latency performance
* guarantee(s).
*
* Copyright (C) 2008-2009 Jon Masters, Red Hat, Inc. <jcm@redhat.com>
* Copyright (C) 2013-2016 Steven Rostedt, Red Hat, Inc. <srostedt@redhat.com>
*
* Includes useful feedback from Clark Williams <clark@redhat.com>
*
* This file is licensed under the terms of the GNU General Public
* License version 2. This program is licensed "as is" without any
* warranty of any kind, whether express or implied.
*/
#include <linux/kthread.h>
#include <linux/tracefs.h>
#include <linux/uaccess.h>
#include <linux/cpumask.h>
#include <linux/delay.h>
#include "trace.h"
static struct trace_array *hwlat_trace;
#define U64STR_SIZE 22 /* 20 digits max */
#define BANNER "hwlat_detector: "
#define DEFAULT_SAMPLE_WINDOW 1000000 /* 1s */
#define DEFAULT_SAMPLE_WIDTH 500000 /* 0.5s */
#define DEFAULT_LAT_THRESHOLD 10 /* 10us */
/* sampling thread*/
static struct task_struct *hwlat_kthread;
static struct dentry *hwlat_sample_width; /* sample width us */
static struct dentry *hwlat_sample_window; /* sample window us */
/* Save the previous tracing_thresh value */
static unsigned long save_tracing_thresh;
/* NMI timestamp counters */
static u64 nmi_ts_start;
static u64 nmi_total_ts;
static int nmi_count;
static int nmi_cpu;
/* Tells NMIs to call back to the hwlat tracer to record timestamps */
bool trace_hwlat_callback_enabled;
/* If the user changed threshold, remember it */
static u64 last_tracing_thresh = DEFAULT_LAT_THRESHOLD * NSEC_PER_USEC;
/* Individual latency samples are stored here when detected. */
struct hwlat_sample {
u64 seqnum; /* unique sequence */
u64 duration; /* delta */
u64 outer_duration; /* delta (outer loop) */
u64 nmi_total_ts; /* Total time spent in NMIs */
struct timespec timestamp; /* wall time */
int nmi_count; /* # NMIs during this sample */
};
/* keep the global state somewhere. */
static struct hwlat_data {
struct mutex lock; /* protect changes */
u64 count; /* total since reset */
u64 sample_window; /* total sampling window (on+off) */
u64 sample_width; /* active sampling portion of window */
} hwlat_data = {
.sample_window = DEFAULT_SAMPLE_WINDOW,
.sample_width = DEFAULT_SAMPLE_WIDTH,
};
static void trace_hwlat_sample(struct hwlat_sample *sample)
{
struct trace_array *tr = hwlat_trace;
struct trace_event_call *call = &event_hwlat;
struct ring_buffer *buffer = tr->trace_buffer.buffer;
struct ring_buffer_event *event;
struct hwlat_entry *entry;
unsigned long flags;
int pc;
pc = preempt_count();
local_save_flags(flags);
event = trace_buffer_lock_reserve(buffer, TRACE_HWLAT, sizeof(*entry),
flags, pc);
if (!event)
return;
entry = ring_buffer_event_data(event);
entry->seqnum = sample->seqnum;
entry->duration = sample->duration;
entry->outer_duration = sample->outer_duration;
entry->timestamp = sample->timestamp;
entry->nmi_total_ts = sample->nmi_total_ts;
entry->nmi_count = sample->nmi_count;
if (!call_filter_check_discard(call, entry, buffer, event))
__buffer_unlock_commit(buffer, event);
}
/* Macros to encapsulate the time capturing infrastructure */
#define time_type u64
#define time_get() trace_clock_local()
#define time_to_us(x) div_u64(x, 1000)
#define time_sub(a, b) ((a) - (b))
#define init_time(a, b) (a = b)
#define time_u64(a) a
void trace_hwlat_callback(bool enter)
{
if (smp_processor_id() != nmi_cpu)
return;
/*
* Currently trace_clock_local() calls sched_clock() and the
* generic version is not NMI safe.
*/
if (!IS_ENABLED(CONFIG_GENERIC_SCHED_CLOCK)) {
if (enter)
nmi_ts_start = time_get();
else
nmi_total_ts = time_get() - nmi_ts_start;
}
if (enter)
nmi_count++;
}
/**
* get_sample - sample the CPU TSC and look for likely hardware latencies
*
* Used to repeatedly capture the CPU TSC (or similar), looking for potential
* hardware-induced latency. Called with interrupts disabled and with
* hwlat_data.lock held.
*/
static int get_sample(void)
{
struct trace_array *tr = hwlat_trace;
time_type start, t1, t2, last_t2;
s64 diff, total, last_total = 0;
u64 sample = 0;
u64 thresh = tracing_thresh;
u64 outer_sample = 0;
int ret = -1;
do_div(thresh, NSEC_PER_USEC); /* modifies interval value */
nmi_cpu = smp_processor_id();
nmi_total_ts = 0;
nmi_count = 0;
/* Make sure NMIs see this first */
barrier();
trace_hwlat_callback_enabled = true;
init_time(last_t2, 0);
start = time_get(); /* start timestamp */
do {
t1 = time_get(); /* we'll look for a discontinuity */
t2 = time_get();
if (time_u64(last_t2)) {
/* Check the delta from outer loop (t2 to next t1) */
diff = time_to_us(time_sub(t1, last_t2));
/* This shouldn't happen */
if (diff < 0) {
pr_err(BANNER "time running backwards\n");
goto out;
}
if (diff > outer_sample)
outer_sample = diff;
}
last_t2 = t2;
total = time_to_us(time_sub(t2, start)); /* sample width */
/* Check for possible overflows */
if (total < last_total) {
pr_err("Time total overflowed\n");
break;
}
last_total = total;
/* This checks the inner loop (t1 to t2) */
diff = time_to_us(time_sub(t2, t1)); /* current diff */
/* This shouldn't happen */
if (diff < 0) {
pr_err(BANNER "time running backwards\n");
goto out;
}
if (diff > sample)
sample = diff; /* only want highest value */
} while (total <= hwlat_data.sample_width);
barrier(); /* finish the above in the view for NMIs */
trace_hwlat_callback_enabled = false;
barrier(); /* Make sure nmi_total_ts is no longer updated */
ret = 0;
/* If we exceed the threshold value, we have found a hardware latency */
if (sample > thresh || outer_sample > thresh) {
struct hwlat_sample s;
ret = 1;
/* We read in microseconds */
if (nmi_total_ts)
do_div(nmi_total_ts, NSEC_PER_USEC);
hwlat_data.count++;
s.seqnum = hwlat_data.count;
s.duration = sample;
s.outer_duration = outer_sample;
s.timestamp = CURRENT_TIME;
s.nmi_total_ts = nmi_total_ts;
s.nmi_count = nmi_count;
trace_hwlat_sample(&s);
/* Keep a running maximum ever recorded hardware latency */
if (sample > tr->max_latency)
tr->max_latency = sample;
}
out:
return ret;
}
static struct cpumask save_cpumask;
static bool disable_migrate;
static void move_to_next_cpu(void)
{
static struct cpumask *current_mask;
int next_cpu;
if (disable_migrate)
return;
/* Just pick the first CPU on first iteration */
if (!current_mask) {
current_mask = &save_cpumask;
get_online_cpus();
cpumask_and(current_mask, cpu_online_mask, tracing_buffer_mask);
put_online_cpus();
next_cpu = cpumask_first(current_mask);
goto set_affinity;
}
/*
* If for some reason the user modifies the CPU affinity
* of this thread, than stop migrating for the duration
* of the current test.
*/
if (!cpumask_equal(current_mask, &current->cpus_allowed))
goto disable;
get_online_cpus();
cpumask_and(current_mask, cpu_online_mask, tracing_buffer_mask);
next_cpu = cpumask_next(smp_processor_id(), current_mask);
put_online_cpus();
if (next_cpu >= nr_cpu_ids)
next_cpu = cpumask_first(current_mask);
set_affinity:
if (next_cpu >= nr_cpu_ids) /* Shouldn't happen! */
goto disable;
cpumask_clear(current_mask);
cpumask_set_cpu(next_cpu, current_mask);
sched_setaffinity(0, current_mask);
return;
disable:
disable_migrate = true;
}
/*
* kthread_fn - The CPU time sampling/hardware latency detection kernel thread
*
* Used to periodically sample the CPU TSC via a call to get_sample. We
* disable interrupts, which does (intentionally) introduce latency since we
* need to ensure nothing else might be running (and thus preempting).
* Obviously this should never be used in production environments.
*
* Currently this runs on which ever CPU it was scheduled on, but most
* real-world hardware latency situations occur across several CPUs,
* but we might later generalize this if we find there are any actualy
* systems with alternate SMI delivery or other hardware latencies.
*/
static int kthread_fn(void *data)
{
u64 interval;
while (!kthread_should_stop()) {
move_to_next_cpu();
local_irq_disable();
get_sample();
local_irq_enable();
mutex_lock(&hwlat_data.lock);
interval = hwlat_data.sample_window - hwlat_data.sample_width;
mutex_unlock(&hwlat_data.lock);
do_div(interval, USEC_PER_MSEC); /* modifies interval value */
/* Always sleep for at least 1ms */
if (interval < 1)
interval = 1;
if (msleep_interruptible(interval))
break;
}
return 0;
}
/**
* start_kthread - Kick off the hardware latency sampling/detector kthread
*
* This starts the kernel thread that will sit and sample the CPU timestamp
* counter (TSC or similar) and look for potential hardware latencies.
*/
static int start_kthread(struct trace_array *tr)
{
struct task_struct *kthread;
kthread = kthread_create(kthread_fn, NULL, "hwlatd");
if (IS_ERR(kthread)) {
pr_err(BANNER "could not start sampling thread\n");
return -ENOMEM;
}
hwlat_kthread = kthread;
wake_up_process(kthread);
return 0;
}
/**
* stop_kthread - Inform the hardware latency samping/detector kthread to stop
*
* This kicks the running hardware latency sampling/detector kernel thread and
* tells it to stop sampling now. Use this on unload and at system shutdown.
*/
static void stop_kthread(void)
{
if (!hwlat_kthread)
return;
kthread_stop(hwlat_kthread);
hwlat_kthread = NULL;
}
/*
* hwlat_read - Wrapper read function for reading both window and width
* @filp: The active open file structure
* @ubuf: The userspace provided buffer to read value into
* @cnt: The maximum number of bytes to read
* @ppos: The current "file" position
*
* This function provides a generic read implementation for the global state
* "hwlat_data" structure filesystem entries.
*/
static ssize_t hwlat_read(struct file *filp, char __user *ubuf,
size_t cnt, loff_t *ppos)
{
char buf[U64STR_SIZE];
u64 *entry = filp->private_data;
u64 val;
int len;
if (!entry)
return -EFAULT;
if (cnt > sizeof(buf))
cnt = sizeof(buf);
val = *entry;
len = snprintf(buf, sizeof(buf), "%llu\n", val);
return simple_read_from_buffer(ubuf, cnt, ppos, buf, len);
}
/**
* hwlat_width_write - Write function for "width" entry
* @filp: The active open file structure
* @ubuf: The user buffer that contains the value to write
* @cnt: The maximum number of bytes to write to "file"
* @ppos: The current position in @file
*
* This function provides a write implementation for the "width" interface
* to the hardware latency detector. It can be used to configure
* for how many us of the total window us we will actively sample for any
* hardware-induced latency periods. Obviously, it is not possible to
* sample constantly and have the system respond to a sample reader, or,
* worse, without having the system appear to have gone out to lunch. It
* is enforced that width is less that the total window size.
*/
static ssize_t
hwlat_width_write(struct file *filp, const char __user *ubuf,
size_t cnt, loff_t *ppos)
{
u64 val;
int err;
err = kstrtoull_from_user(ubuf, cnt, 10, &val);
if (err)
return err;
mutex_lock(&hwlat_data.lock);
if (val < hwlat_data.sample_window)
hwlat_data.sample_width = val;
else
err = -EINVAL;
mutex_unlock(&hwlat_data.lock);
if (err)
return err;
return cnt;
}
/**
* hwlat_window_write - Write function for "window" entry
* @filp: The active open file structure
* @ubuf: The user buffer that contains the value to write
* @cnt: The maximum number of bytes to write to "file"
* @ppos: The current position in @file
*
* This function provides a write implementation for the "window" interface
* to the hardware latency detetector. The window is the total time
* in us that will be considered one sample period. Conceptually, windows
* occur back-to-back and contain a sample width period during which
* actual sampling occurs. Can be used to write a new total window size. It
* is enfoced that any value written must be greater than the sample width
* size, or an error results.
*/
static ssize_t
hwlat_window_write(struct file *filp, const char __user *ubuf,
size_t cnt, loff_t *ppos)
{
u64 val;
int err;
err = kstrtoull_from_user(ubuf, cnt, 10, &val);
if (err)
return err;
mutex_lock(&hwlat_data.lock);
if (hwlat_data.sample_width < val)
hwlat_data.sample_window = val;
else
err = -EINVAL;
mutex_unlock(&hwlat_data.lock);
if (err)
return err;
return cnt;
}
static const struct file_operations width_fops = {
.open = tracing_open_generic,
.read = hwlat_read,
.write = hwlat_width_write,
};
static const struct file_operations window_fops = {
.open = tracing_open_generic,
.read = hwlat_read,
.write = hwlat_window_write,
};
/**
* init_tracefs - A function to initialize the tracefs interface files
*
* This function creates entries in tracefs for "hwlat_detector".
* It creates the hwlat_detector directory in the tracing directory,
* and within that directory is the count, width and window files to
* change and view those values.
*/
static int init_tracefs(void)
{
struct dentry *d_tracer;
struct dentry *top_dir;
d_tracer = tracing_init_dentry();
if (IS_ERR(d_tracer))
return -ENOMEM;
top_dir = tracefs_create_dir("hwlat_detector", d_tracer);
if (!top_dir)
return -ENOMEM;
hwlat_sample_window = tracefs_create_file("window", 0640,
top_dir,
&hwlat_data.sample_window,
&window_fops);
if (!hwlat_sample_window)
goto err;
hwlat_sample_width = tracefs_create_file("width", 0644,
top_dir,
&hwlat_data.sample_width,
&width_fops);
if (!hwlat_sample_width)
goto err;
return 0;
err:
tracefs_remove_recursive(top_dir);
return -ENOMEM;
}
static void hwlat_tracer_start(struct trace_array *tr)
{
int err;
err = start_kthread(tr);
if (err)
pr_err(BANNER "Cannot start hwlat kthread\n");
}
static void hwlat_tracer_stop(struct trace_array *tr)
{
stop_kthread();
}
static bool hwlat_busy;
static int hwlat_tracer_init(struct trace_array *tr)
{
/* Only allow one instance to enable this */
if (hwlat_busy)
return -EBUSY;
hwlat_trace = tr;
disable_migrate = false;
hwlat_data.count = 0;
tr->max_latency = 0;
save_tracing_thresh = tracing_thresh;
/* tracing_thresh is in nsecs, we speak in usecs */
if (!tracing_thresh)
tracing_thresh = last_tracing_thresh;
if (tracer_tracing_is_on(tr))
hwlat_tracer_start(tr);
hwlat_busy = true;
return 0;
}
static void hwlat_tracer_reset(struct trace_array *tr)
{
stop_kthread();
/* the tracing threshold is static between runs */
last_tracing_thresh = tracing_thresh;
tracing_thresh = save_tracing_thresh;
hwlat_busy = false;
}
static struct tracer hwlat_tracer __read_mostly =
{
.name = "hwlat",
.init = hwlat_tracer_init,
.reset = hwlat_tracer_reset,
.start = hwlat_tracer_start,
.stop = hwlat_tracer_stop,
.allow_instances = true,
};
__init static int init_hwlat_tracer(void)
{
int ret;
mutex_init(&hwlat_data.lock);
ret = register_tracer(&hwlat_tracer);
if (ret)
return ret;
init_tracefs();
return 0;
}
late_initcall(init_hwlat_tracer);

66
kernel/trace/trace_output.c
View File

@ -1098,6 +1098,71 @@ static struct trace_event trace_user_stack_event = {
.funcs = &trace_user_stack_funcs,
};
/* TRACE_HWLAT */
static enum print_line_t
trace_hwlat_print(struct trace_iterator *iter, int flags,
struct trace_event *event)
{
struct trace_entry *entry = iter->ent;
struct trace_seq *s = &iter->seq;
struct hwlat_entry *field;
trace_assign_type(field, entry);
trace_seq_printf(s, "#%-5u inner/outer(us): %4llu/%-5llu ts:%ld.%09ld",
field->seqnum,
field->duration,
field->outer_duration,
field->timestamp.tv_sec,
field->timestamp.tv_nsec);
if (field->nmi_count) {
/*
* The generic sched_clock() is not NMI safe, thus
* we only record the count and not the time.
*/
if (!IS_ENABLED(CONFIG_GENERIC_SCHED_CLOCK))
trace_seq_printf(s, " nmi-total:%llu",
field->nmi_total_ts);
trace_seq_printf(s, " nmi-count:%u",
field->nmi_count);
}
trace_seq_putc(s, '\n');
return trace_handle_return(s);
}
static enum print_line_t
trace_hwlat_raw(struct trace_iterator *iter, int flags,
struct trace_event *event)
{
struct hwlat_entry *field;
struct trace_seq *s = &iter->seq;
trace_assign_type(field, iter->ent);
trace_seq_printf(s, "%llu %lld %ld %09ld %u\n",
field->duration,
field->outer_duration,
field->timestamp.tv_sec,
field->timestamp.tv_nsec,
field->seqnum);
return trace_handle_return(s);
}
static struct trace_event_functions trace_hwlat_funcs = {
.trace = trace_hwlat_print,
.raw = trace_hwlat_raw,
};
static struct trace_event trace_hwlat_event = {
.type = TRACE_HWLAT,
.funcs = &trace_hwlat_funcs,
};
/* TRACE_BPUTS */
static enum print_line_t
trace_bputs_print(struct trace_iterator *iter, int flags,
@ -1233,6 +1298,7 @@ static struct trace_event *events[] __initdata = {
&trace_bputs_event,
&trace_bprint_event,
&trace_print_event,
&trace_hwlat_event,
NULL
};

4
kernel/trace/trace_uprobe.c
View File

@ -431,10 +431,6 @@ static int create_trace_uprobe(int argc, char **argv)
pr_info("Probe point is not specified.\n");
return -EINVAL;
}
if (isdigit(argv[1][0])) {
pr_info("probe point must be have a filename.\n");
return -EINVAL;
}
arg = strchr(argv[1], ':');
if (!arg) {
ret = -EINVAL;

115
scripts/tracing/ftrace-bisect.sh Executable file
View File

@ -0,0 +1,115 @@
#!/bin/bash
#
# Here's how to use this:
#
# This script is used to help find functions that are being traced by function
# tracer or function graph tracing that causes the machine to reboot, hang, or
# crash. Here's the steps to take.
#
# First, determine if function tracing is working with a single function:
#
# (note, if this is a problem with function_graph tracing, then simply
# replace "function" with "function_graph" in the following steps).
#
# # cd /sys/kernel/debug/tracing
# # echo schedule > set_ftrace_filter
# # echo function > current_tracer
#
# If this works, then we know that something is being traced that shouldn't be.
#
# # echo nop > current_tracer
#
# # cat available_filter_functions > ~/full-file
# # ftrace-bisect ~/full-file ~/test-file ~/non-test-file
# # cat ~/test-file > set_ftrace_filter
#
# *** Note *** this will take several minutes. Setting multiple functions is
# an O(n^2) operation, and we are dealing with thousands of functions. So go
# have coffee, talk with your coworkers, read facebook. And eventually, this
# operation will end.
#
# # echo function > current_tracer
#
# If it crashes, we know that ~/test-file has a bad function.
#
# Reboot back to test kernel.
#
# # cd /sys/kernel/debug/tracing
# # mv ~/test-file ~/full-file
#
# If it didn't crash.
#
# # echo nop > current_tracer
# # mv ~/non-test-file ~/full-file
#
# Get rid of the other test file from previous run (or save them off somewhere).
# # rm -f ~/test-file ~/non-test-file
#
# And start again:
#
# # ftrace-bisect ~/full-file ~/test-file ~/non-test-file
#
# The good thing is, because this cuts the number of functions in ~/test-file
# by half, the cat of it into set_ftrace_filter takes half as long each
# iteration, so don't talk so much at the water cooler the second time.
#
# Eventually, if you did this correctly, you will get down to the problem
# function, and all we need to do is to notrace it.
#
# The way to figure out if the problem function is bad, just do:
#
# # echo <problem-function> > set_ftrace_notrace
# # echo > set_ftrace_filter
# # echo function > current_tracer
#
# And if it doesn't crash, we are done.
#
# If it does crash, do this again (there's more than one problem function)
# but you need to echo the problem function(s) into set_ftrace_notrace before
# enabling function tracing in the above steps. Or if you can compile the
# kernel, annotate the problem functions with "notrace" and start again.
#
if [ $# -ne 3 ]; then
echo 'usage: ftrace-bisect full-file test-file non-test-file'
exit
fi
full=$1
test=$2
nontest=$3
x=`cat $full | wc -l`
if [ $x -eq 1 ]; then
echo "There's only one function left, must be the bad one"
cat $full
exit 0
fi
let x=$x/2
let y=$x+1
if [ ! -f $full ]; then
echo "$full does not exist"
exit 1
fi
if [ -f $test ]; then
echo -n "$test exists, delete it? [y/N]"
read a
if [ "$a" != "y" -a "$a" != "Y" ]; then
exit 1
fi
fi
if [ -f $nontest ]; then
echo -n "$nontest exists, delete it? [y/N]"
read a
if [ "$a" != "y" -a "$a" != "Y" ]; then
exit 1
fi
fi
sed -ne "1,${x}p" $full > $test
sed -ne "$y,\$p" $full > $nontest