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perf/core: Use static_call to optimize perf_guest_info_callbacks

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Use static_call to optimize perf's guest callbacks on arm64 and x86,
which are now the only architectures that define the callbacks.  Use
DEFINE_STATIC_CALL_RET0 as the default/NULL for all guest callbacks, as
the callback semantics are that a return value '0' means "not in guest".

static_call obviously avoids the overhead of CONFIG_RETPOLINE=y, but is
also advantageous versus other solutions, e.g. per-cpu callbacks, in that
a per-cpu memory load is not needed to detect the !guest case.

Based on code from Peter and Like.

Suggested-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Link: https://lore.kernel.org/r/20211111020738.2512932-10-seanjc@google.com
This commit is contained in:
Sean Christopherson 2021-11-11 02:07:30 +00:00 committed by Peter Zijlstra
parent 2aef6f306b
commit 87b940a067
2 changed files with 23 additions and 26 deletions
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34
include/linux/perf_event.h
View File

@ -1244,40 +1244,22 @@ extern void perf_event_bpf_event(struct bpf_prog *prog,
#ifdef CONFIG_GUEST_PERF_EVENTS
extern struct perf_guest_info_callbacks __rcu *perf_guest_cbs;
static inline struct perf_guest_info_callbacks *perf_get_guest_cbs(void)
{
/*
* Callbacks are RCU-protected and must be READ_ONCE to avoid reloading
* the callbacks between a !NULL check and dereferences, to ensure
* pending stores/changes to the callback pointers are visible before a
* non-NULL perf_guest_cbs is visible to readers, and to prevent a
* module from unloading callbacks while readers are active.
*/
return rcu_dereference(perf_guest_cbs);
}
DECLARE_STATIC_CALL(__perf_guest_state, *perf_guest_cbs->state);
DECLARE_STATIC_CALL(__perf_guest_get_ip, *perf_guest_cbs->get_ip);
DECLARE_STATIC_CALL(__perf_guest_handle_intel_pt_intr, *perf_guest_cbs->handle_intel_pt_intr);
static inline unsigned int perf_guest_state(void)
{
struct perf_guest_info_callbacks *guest_cbs = perf_get_guest_cbs();
return guest_cbs ? guest_cbs->state() : 0;
return static_call(__perf_guest_state)();
}
static inline unsigned long perf_guest_get_ip(void)
{
struct perf_guest_info_callbacks *guest_cbs = perf_get_guest_cbs();
/*
* Arbitrarily return '0' in the unlikely scenario that the callbacks
* are unregistered between checking guest state and getting the IP.
*/
return guest_cbs ? guest_cbs->get_ip() : 0;
return static_call(__perf_guest_get_ip)();
}
static inline unsigned int perf_guest_handle_intel_pt_intr(void)
{
struct perf_guest_info_callbacks *guest_cbs = perf_get_guest_cbs();
if (guest_cbs && guest_cbs->handle_intel_pt_intr)
return guest_cbs->handle_intel_pt_intr();
return 0;
return static_call(__perf_guest_handle_intel_pt_intr)();
}
extern void perf_register_guest_info_callbacks(struct perf_guest_info_callbacks *cbs);
extern void perf_unregister_guest_info_callbacks(struct perf_guest_info_callbacks *cbs);

15
kernel/events/core.c
View File

@ -6524,12 +6524,23 @@ static void perf_pending_event(struct irq_work *entry)
#ifdef CONFIG_GUEST_PERF_EVENTS
struct perf_guest_info_callbacks __rcu *perf_guest_cbs;
DEFINE_STATIC_CALL_RET0(__perf_guest_state, *perf_guest_cbs->state);
DEFINE_STATIC_CALL_RET0(__perf_guest_get_ip, *perf_guest_cbs->get_ip);
DEFINE_STATIC_CALL_RET0(__perf_guest_handle_intel_pt_intr, *perf_guest_cbs->handle_intel_pt_intr);
void perf_register_guest_info_callbacks(struct perf_guest_info_callbacks *cbs)
{
if (WARN_ON_ONCE(rcu_access_pointer(perf_guest_cbs)))
return;
rcu_assign_pointer(perf_guest_cbs, cbs);
static_call_update(__perf_guest_state, cbs->state);
static_call_update(__perf_guest_get_ip, cbs->get_ip);
/* Implementing ->handle_intel_pt_intr is optional. */
if (cbs->handle_intel_pt_intr)
static_call_update(__perf_guest_handle_intel_pt_intr,
cbs->handle_intel_pt_intr);
}
EXPORT_SYMBOL_GPL(perf_register_guest_info_callbacks);
@ -6539,6 +6550,10 @@ void perf_unregister_guest_info_callbacks(struct perf_guest_info_callbacks *cbs)
return;
rcu_assign_pointer(perf_guest_cbs, NULL);
static_call_update(__perf_guest_state, (void *)&__static_call_return0);
static_call_update(__perf_guest_get_ip, (void *)&__static_call_return0);
static_call_update(__perf_guest_handle_intel_pt_intr,
(void *)&__static_call_return0);
synchronize_rcu();
}
EXPORT_SYMBOL_GPL(perf_unregister_guest_info_callbacks);