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| author | Mikołaj Kołek <kolek.mikolaj@gmail.com> | 2024-07-02 21:19:28 +0200 |
|---|---|---|
| committer | Alejandro Colomar <alx@kernel.org> | 2024-07-09 14:28:13 +0200 |
| commit | 0f1f2327069d0c0ebb1f090ca1a183ca51de75f2 (patch) | |
| tree | 092e6d2904e0f649fff763e0976cb2bbd2482250 | |
| parent | 346bb648cc963bd9f2c8b16d984cb49030faa05b (diff) | |
| download | man-pages-0f1f2327069d0c0ebb1f090ca1a183ca51de75f2.tar.gz | |
perf_event_open.2: Document combining inherit and cpus = -1 preventing the use of mmap
After calling perf_event_open() with cpus == -1 and the inherit bit,
using mmap on the perf file descriptor to create a ring-buffer fails
with EINVAL. This behavior wasn't previously documented in the man
page and is caused by the following lines in the perf_mmap function in
<kernel/events/core.c>:
/*
* Don't allow mmap() of inherited per-task counters. This would
* create a performance issue due to all children writing to the
* same rb.
*/
if (event->cpu == -1 && event->attr.inherit)
return -EINVAL;
Signed-off-by: Mikołaj Kołek <kolek.mikolaj@gmail.com>
Message-ID: <CAHGiy6-nx0PwBi6xwoG8PN5qND-krGh_rvpfmVc31-QSv04C6g@mail.gmail.com>
Signed-off-by: Alejandro Colomar <alx@kernel.org>
| -rw-r--r-- | man/man2/perf_event_open.2 | 4 |
1 files changed, 4 insertions, 0 deletions
diff --git a/man/man2/perf_event_open.2 b/man/man2/perf_event_open.2 index 15411027d7..72d8fd7971 100644 --- a/man/man2/perf_event_open.2 +++ b/man/man2/perf_event_open.2 @@ -1027,6 +1027,10 @@ Inherit does not work for some combinations of .I read_format values, such as .BR PERF_FORMAT_GROUP . +Additionally, using it together with +.I cpu == \-1 +prevents the creation of the mmap ring-buffer used for +logging asynchronous events in sampled mode. .TP .I pinned The |