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Revert "perf: Avoid the read if the count is already updated"

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This reverts commit e1c3bfe365 which is
commit 8ce939a0fa194939cc1f92dbd8bc1a7806e7d40a upstream.

It breaks the Android kernel abi and can be brought back in the future
in an abi-safe way if it is really needed.

Bug: 161946584
Change-Id: I9c672a97df39e7381e10c7cf113a5a36f76c90e4
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>
This commit is contained in:
Greg Kroah-Hartman
2025-06-05 14:27:18 +00:00
parent f4b979262f
commit 22d163151d
3 changed files with 18 additions and 24 deletions
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8
include/linux/perf_event.h
View File

@@ -937,13 +937,7 @@ struct perf_output_handle {
struct perf_buffer *rb;
unsigned long wakeup;
unsigned long size;
union {
u64 flags; /* perf_output*() */
u64 aux_flags; /* perf_aux_output*() */
struct {
u64 skip_read : 1;
};
};
u64 aux_flags;
union {
void *addr;
unsigned long head;

33
kernel/events/core.c
View File

@@ -1180,12 +1180,6 @@ static void perf_event_ctx_deactivate(struct perf_event_context *ctx)
list_del_init(&ctx->active_ctx_list);
}
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);
@@ -3395,7 +3389,8 @@ 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.
*/
perf_pmu_read(event);
if (event->state == PERF_EVENT_STATE_ACTIVE)
event->pmu->read(event);
perf_event_update_time(event);
@@ -4449,8 +4444,15 @@ static void __perf_event_read(void *info)
pmu->read(event);
for_each_sibling_event(sub, event)
perf_pmu_read(sub);
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);
}
}
data->ret = pmu->commit_txn(pmu);
@@ -7050,8 +7052,9 @@ 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) && !handle->skip_read)
perf_pmu_read(leader);
if ((leader != event) &&
(leader->state == PERF_EVENT_STATE_ACTIVE))
leader->pmu->read(leader);
values[n++] = perf_event_count(leader);
if (read_format & PERF_FORMAT_ID)
@@ -7064,8 +7067,9 @@ static void perf_output_read_group(struct perf_output_handle *handle,
for_each_sibling_event(sub, leader) {
n = 0;
if ((sub != event) && !handle->skip_read)
perf_pmu_read(sub);
if ((sub != event) &&
(sub->state == PERF_EVENT_STATE_ACTIVE))
sub->pmu->read(sub);
values[n++] = perf_event_count(sub);
if (read_format & PERF_FORMAT_ID)
@@ -7120,9 +7124,6 @@ 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

@@ -181,7 +181,6 @@ __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)) {