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perf/core: Add a new read format to get a number of lost samples

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[ Upstream commit 119a784c81270eb88e573174ed2209225d646656 ]

Sometimes we want to know an accurate number of samples even if it's
lost.  Currenlty PERF_RECORD_LOST is generated for a ring-buffer which
might be shared with other events.  So it's hard to know per-event
lost count.

Add event->lost_samples field and PERF_FORMAT_LOST to retrieve it from
userspace.

Original-patch-by: Jiri Olsa <[email protected]>
Signed-off-by: Namhyung Kim <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Link: https://lkml.kernel.org/r/[email protected]
Stable-dep-of: 382c27f4ed28 ("perf: Fix perf_event_validate_size()")
Signed-off-by: Sasha Levin <[email protected]>
This commit is contained in:
Namhyung Kim 2022-06-16 11:06:23 -07:00 • committed by Greg Kroah-Hartman
commit 84ca356ec8
4 changed files with 28 additions and 5 deletions
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21
kernel/events/core.c
View file

@ -1726,6 +1726,9 @@ static void __perf_event_read_size(struct perf_event *event, int nr_siblings)
if (event->attr.read_format & PERF_FORMAT_ID)
entry += sizeof(u64);
if (event->attr.read_format & PERF_FORMAT_LOST)
entry += sizeof(u64);
if (event->attr.read_format & PERF_FORMAT_GROUP) {
nr += nr_siblings;
size += sizeof(u64);
@ -4915,11 +4918,15 @@ static int __perf_read_group_add(struct perf_event *leader,
values[n++] += perf_event_count(leader);
if (read_format & PERF_FORMAT_ID)
values[n++] = primary_event_id(leader);
if (read_format & PERF_FORMAT_LOST)
values[n++] = atomic64_read(&leader->lost_samples);
for_each_sibling_event(sub, leader) {
values[n++] += perf_event_count(sub);
if (read_format & PERF_FORMAT_ID)
values[n++] = primary_event_id(sub);
if (read_format & PERF_FORMAT_LOST)
values[n++] = atomic64_read(&sub->lost_samples);
}
unlock:
@ -4973,7 +4980,7 @@ static int perf_read_one(struct perf_event *event,
u64 read_format, char __user *buf)
{
u64 enabled, running;
u64 values[4];
u64 values[5];
int n = 0;
values[n++] = __perf_event_read_value(event, &enabled, &running);
@ -4983,6 +4990,8 @@ static int perf_read_one(struct perf_event *event,
values[n++] = running;
if (read_format & PERF_FORMAT_ID)
values[n++] = primary_event_id(event);
if (read_format & PERF_FORMAT_LOST)
values[n++] = atomic64_read(&event->lost_samples);
if (copy_to_user(buf, values, n * sizeof(u64)))
return -EFAULT;
@ -6312,7 +6321,7 @@ static void perf_output_read_one(struct perf_output_handle *handle,
u64 enabled, u64 running)
{
u64 read_format = event->attr.read_format;
u64 values[4];
u64 values[5];
int n = 0;
values[n++] = perf_event_count(event);
@ -6326,6 +6335,8 @@ static void perf_output_read_one(struct perf_output_handle *handle,
}
if (read_format & PERF_FORMAT_ID)
values[n++] = primary_event_id(event);
if (read_format & PERF_FORMAT_LOST)
values[n++] = atomic64_read(&event->lost_samples);
__output_copy(handle, values, n * sizeof(u64));
}
@ -6336,7 +6347,7 @@ static void perf_output_read_group(struct perf_output_handle *handle,
{
struct perf_event *leader = event->group_leader, *sub;
u64 read_format = event->attr.read_format;
u64 values[5];
u64 values[6];
int n = 0;
values[n++] = 1 + leader->nr_siblings;
@ -6354,6 +6365,8 @@ static void perf_output_read_group(struct perf_output_handle *handle,
values[n++] = perf_event_count(leader);
if (read_format & PERF_FORMAT_ID)
values[n++] = primary_event_id(leader);
if (read_format & PERF_FORMAT_LOST)
values[n++] = atomic64_read(&leader->lost_samples);
__output_copy(handle, values, n * sizeof(u64));
@ -6367,6 +6380,8 @@ static void perf_output_read_group(struct perf_output_handle *handle,
values[n++] = perf_event_count(sub);
if (read_format & PERF_FORMAT_ID)
values[n++] = primary_event_id(sub);
if (read_format & PERF_FORMAT_LOST)
values[n++] = atomic64_read(&sub->lost_samples);
__output_copy(handle, values, n * sizeof(u64));
}

5
kernel/events/ring_buffer.c
View file

@ -171,8 +171,10 @@ __perf_output_begin(struct perf_output_handle *handle,
goto out;
if (unlikely(rb->paused)) {
if (rb->nr_pages)
if (rb->nr_pages) {
local_inc(&rb->lost);
atomic64_inc(&event->lost_samples);
}
goto out;
}
@ -255,6 +257,7 @@ __perf_output_begin(struct perf_output_handle *handle,
fail:
local_inc(&rb->lost);
atomic64_inc(&event->lost_samples);
perf_output_put_handle(handle);
out:
rcu_read_unlock();