From: "Peter Zijlstra (Intel)" peterz@infradead.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@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: Sasha Levin sashal@kernel.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)) {