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Message-Id: <20250505221419.2672473-560-sashal@kernel.org>
Date: Mon, 5 May 2025 18:12:56 -0400
From: Sasha Levin <sashal@...nel.org>
To: linux-kernel@...r.kernel.org,
stable@...r.kernel.org
Cc: "Peter Zijlstra (Intel)" <peterz@...radead.org>,
Kan Liang <kan.liang@...ux.intel.com>,
Sasha Levin <sashal@...nel.org>,
mingo@...hat.com,
acme@...nel.org,
namhyung@...nel.org,
linux-perf-users@...r.kernel.org
Subject: [PATCH AUTOSEL 6.14 560/642] perf: Avoid the read if the count is already updated
From: "Peter Zijlstra (Intel)" <peterz@...radead.org>
[ Upstream commit 8ce939a0fa194939cc1f92dbd8bc1a7806e7d40a ]
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@...radead.org>
Signed-off-by: Kan Liang <kan.liang@...ux.intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Link: https://lkml.kernel.org/r/20250121152303.3128733-3-kan.liang@linux.intel.com
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
include/linux/perf_event.h | 8 +++++++-
kernel/events/core.c | 33 ++++++++++++++++-----------------
kernel/events/ring_buffer.c | 1 +
3 files changed, 24 insertions(+), 18 deletions(-)
diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index 93ea9c6672f0e..3d5814c6d251c 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -1098,7 +1098,13 @@ 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;
diff --git a/kernel/events/core.c b/kernel/events/core.c
index dda1670b3539a..6fa70b3826d0e 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -1191,6 +1191,12 @@ 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);
@@ -3478,8 +3484,7 @@ 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);
@@ -4625,15 +4630,8 @@ 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);
@@ -7451,9 +7449,8 @@ 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)
@@ -7466,9 +7463,8 @@ 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)
@@ -7527,6 +7523,9 @@ 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)
diff --git a/kernel/events/ring_buffer.c b/kernel/events/ring_buffer.c
index 09459647cb822..5130b119d0ae0 100644
--- a/kernel/events/ring_buffer.c
+++ b/kernel/events/ring_buffer.c
@@ -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)) {
--
2.39.5
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