qiurui
/
Centos-kernel-stream-9
mirror of https://gitlab.com/redhat/centos-stream/src/kernel/centos-stream-9.git
1
0
Fork 0
Code Issues Packages Projects Releases Wiki Activity

perf: Avoid the read if the count is already updated 

JIRA: https://issues.redhat.com/browse/RHEL-47444

upstream
========
commit 8ce939a0fa194939cc1f92dbd8bc1a7806e7d40a
Author: Peter Zijlstra (Intel) <peterz@infradead.org>
Date: Tue Jan 21 07:23:02 2025 -0800

description
===========
The event may have been updated in the PMU-specific implementation,
e.g., Intel PEBS counters snapshotting. The common code should not
read and overwrite the value.

The PERF_SAMPLE_READ in the data->sample_type can be used to detect
whether the PMU-specific value is available. If yes, avoid the
pmu->read() in the common code. Add a new flag, skip_read, to track the
case.

Factor out a perf_pmu_read() to clean up the code.

    Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
    Signed-off-by: Kan Liang <kan.liang@linux.intel.com>
    Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
    Link: https://lkml.kernel.org/r/20250121152303.3128733-3-kan.liang@linux.intel.com

Signed-off-by: Michael Petlan <mpetlan@redhat.com>
This commit is contained in:
Michael Petlan 2025-05-19 11:28:40 +02:00
parent f8df95796d
commit 03491643b6
3 changed files with 24 additions and 18 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

8
include/linux/perf_event.h
View File

@ -1041,7 +1041,13 @@ struct perf_output_handle {
struct perf_buffer *rb;
unsigned long wakeup;
unsigned long size;
u64 aux_flags;
union {
u64 flags; /* perf_output*() */
u64 aux_flags; /* perf_aux_output*() */
struct {
u64 skip_read : 1;
};
};
union {
void *addr;
unsigned long head;

33
kernel/events/core.c
View File

@ -1195,6 +1195,12 @@ static void perf_assert_pmu_disabled(struct pmu *pmu)
WARN_ON_ONCE(*this_cpu_ptr(pmu->pmu_disable_count) == 0);
}
static inline void perf_pmu_read(struct perf_event *event)
{
if (event->state == PERF_EVENT_STATE_ACTIVE)
event->pmu->read(event);
}
static void get_ctx(struct perf_event_context *ctx)
{
refcount_inc(&ctx->refcount);
@ -3473,8 +3479,7 @@ static void __perf_event_sync_stat(struct perf_event *event,
* we know the event must be on the current CPU, therefore we
* don't need to use it.
*/
if (event->state == PERF_EVENT_STATE_ACTIVE)
event->pmu->read(event);
perf_pmu_read(event);
perf_event_update_time(event);
@ -4624,15 +4629,8 @@ static void __perf_event_read(void *info)
pmu->read(event);
for_each_sibling_event(sub, event) {
if (sub->state == PERF_EVENT_STATE_ACTIVE) {
/*
* Use sibling's PMU rather than @event's since
* sibling could be on different (eg: software) PMU.
*/
sub->pmu->read(sub);
}
}
for_each_sibling_event(sub, event)
perf_pmu_read(sub);
data->ret = pmu->commit_txn(pmu);
@ -7399,9 +7397,8 @@ static void perf_output_read_group(struct perf_output_handle *handle,
if (read_format & PERF_FORMAT_TOTAL_TIME_RUNNING)
values[n++] = running;
if ((leader != event) &&
(leader->state == PERF_EVENT_STATE_ACTIVE))
leader->pmu->read(leader);
if ((leader != event) && !handle->skip_read)
perf_pmu_read(leader);
values[n++] = perf_event_count(leader, self);
if (read_format & PERF_FORMAT_ID)
@ -7414,9 +7411,8 @@ static void perf_output_read_group(struct perf_output_handle *handle,
for_each_sibling_event(sub, leader) {
n = 0;
if ((sub != event) &&
(sub->state == PERF_EVENT_STATE_ACTIVE))
sub->pmu->read(sub);
if ((sub != event) && !handle->skip_read)
perf_pmu_read(sub);
values[n++] = perf_event_count(sub, self);
if (read_format & PERF_FORMAT_ID)
@ -7475,6 +7471,9 @@ void perf_output_sample(struct perf_output_handle *handle,
{
u64 sample_type = data->type;
if (data->sample_flags & PERF_SAMPLE_READ)
handle->skip_read = 1;
perf_output_put(handle, *header);
if (sample_type & PERF_SAMPLE_IDENTIFIER)

1
kernel/events/ring_buffer.c
View File

@ -185,6 +185,7 @@ __perf_output_begin(struct perf_output_handle *handle,
handle->rb = rb;
handle->event = event;
handle->flags = 0;
have_lost = local_read(&rb->lost);
if (unlikely(have_lost)) {