From: Stephane Eranian <eranian@google.com>
To: Jiri Olsa <jolsa@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>,
Peter Zijlstra <peterz@infradead.org>,
Ingo Molnar <mingo@kernel.org>,
Arnaldo Carvalho de Melo <acme@kernel.org>,
Mark Rutland <mark.rutland@arm.com>,
Alexander Shishkin <alexander.shishkin@linux.intel.com>,
LKML <linux-kernel@vger.kernel.org>,
Andi Kleen <ak@linux.intel.com>, Ian Rogers <irogers@google.com>,
gmx@google.com
Subject: Re: [RFC] perf/core: Add an ioctl to get a number of lost samples
Date: Wed, 11 Aug 2021 12:33:38 -0700 [thread overview]
Message-ID: <CABPqkBQGu5Xb=PbwjfwQxmp5nVuZZ6tg4LnZaKJConYWkPcL2g@mail.gmail.com> (raw)
In-Reply-To: <YRPnCLyn9oE540gM@krava>
On Wed, Aug 11, 2021 at 8:04 AM Jiri Olsa <jolsa@redhat.com> wrote:
>
> On Tue, Aug 10, 2021 at 11:21:35PM -0700, Namhyung Kim wrote:
> > 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_EVENT_IOC_LOST_SAMPLES to
> > retrieve it from userspace.
> >
> > Signed-off-by: Namhyung Kim <namhyung@kernel.org>
> > ---
> > include/linux/perf_event.h | 2 ++
> > include/uapi/linux/perf_event.h | 1 +
> > kernel/events/core.c | 9 +++++++++
> > kernel/events/ring_buffer.c | 5 ++++-
> > 4 files changed, 16 insertions(+), 1 deletion(-)
> >
> > diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
> > index f5a6a2f069ed..44d72079c77a 100644
> > --- a/include/linux/perf_event.h
> > +++ b/include/linux/perf_event.h
> > @@ -756,6 +756,8 @@ struct perf_event {
> > struct pid_namespace *ns;
> > u64 id;
> >
> > + atomic_t lost_samples;
> > +
> > u64 (*clock)(void);
> > perf_overflow_handler_t overflow_handler;
> > void *overflow_handler_context;
> > diff --git a/include/uapi/linux/perf_event.h b/include/uapi/linux/perf_event.h
> > index bf8143505c49..24397799127d 100644
> > --- a/include/uapi/linux/perf_event.h
> > +++ b/include/uapi/linux/perf_event.h
> > @@ -505,6 +505,7 @@ struct perf_event_query_bpf {
> > #define PERF_EVENT_IOC_PAUSE_OUTPUT _IOW('$', 9, __u32)
> > #define PERF_EVENT_IOC_QUERY_BPF _IOWR('$', 10, struct perf_event_query_bpf *)
> > #define PERF_EVENT_IOC_MODIFY_ATTRIBUTES _IOW('$', 11, struct perf_event_attr *)
> > +#define PERF_EVENT_IOC_LOST_SAMPLES _IOR('$', 12, __u64 *)
>
> would it be better to use the read syscall for that?
> https://lore.kernel.org/lkml/20210622153918.688500-5-jolsa@kernel.org/
>
> that patchset ended up on me not having a way to reproduce the
> issue you guys wanted the fix for ;-) the lost count is there
> as well
>
Does the read format approach succeed even when the event is in error state?
> jirka
>
> >
> > enum perf_event_ioc_flags {
> > PERF_IOC_FLAG_GROUP = 1U << 0,
> > diff --git a/kernel/events/core.c b/kernel/events/core.c
> > index 0e125ae2fa92..a4d6736b6594 100644
> > --- a/kernel/events/core.c
> > +++ b/kernel/events/core.c
> > @@ -5664,6 +5664,15 @@ static long _perf_ioctl(struct perf_event *event, unsigned int cmd, unsigned lon
> >
> > return perf_event_modify_attr(event, &new_attr);
> > }
> > +
> > + case PERF_EVENT_IOC_LOST_SAMPLES: {
> > + u64 lost = atomic_read(&event->lost_samples);
> > +
> > + if (copy_to_user((void __user *)arg, &lost, sizeof(lost)))
> > + return -EFAULT;
> > + return 0;
> > + }
> > +
> > default:
> > return -ENOTTY;
> > }
> > diff --git a/kernel/events/ring_buffer.c b/kernel/events/ring_buffer.c
> > index 52868716ec35..06d7dacb05da 100644
> > --- a/kernel/events/ring_buffer.c
> > +++ b/kernel/events/ring_buffer.c
> > @@ -172,8 +172,10 @@ __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);
> > + atomic_inc(&event->lost_samples);
> > + }
> > goto out;
> > }
> >
> > @@ -254,6 +256,7 @@ __perf_output_begin(struct perf_output_handle *handle,
> >
> > fail:
> > local_inc(&rb->lost);
> > + atomic_inc(&event->lost_samples);
> > perf_output_put_handle(handle);
> > out:
> > rcu_read_unlock();
> > --
> > 2.32.0.605.g8dce9f2422-goog
> >
>
next prev parent reply other threads:[~2021-08-11 19:33 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-08-11 6:21 [RFC] perf/core: Add an ioctl to get a number of lost samples Namhyung Kim
2021-08-11 13:12 ` Andi Kleen
2021-08-11 15:04 ` Jiri Olsa
2021-08-11 19:33 ` Stephane Eranian [this message]
2021-08-11 19:57 ` Jiri Olsa
2021-08-11 20:57 ` Namhyung Kim
2021-08-11 23:57 ` Stephane Eranian
2021-08-11 20:54 ` Namhyung Kim
2021-08-24 14:02 ` Peter Zijlstra
2021-08-24 17:55 ` Namhyung Kim
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to='CABPqkBQGu5Xb=PbwjfwQxmp5nVuZZ6tg4LnZaKJConYWkPcL2g@mail.gmail.com' \
--to=eranian@google.com \
--cc=acme@kernel.org \
--cc=ak@linux.intel.com \
--cc=alexander.shishkin@linux.intel.com \
--cc=gmx@google.com \
--cc=irogers@google.com \
--cc=jolsa@redhat.com \
--cc=linux-kernel@vger.kernel.org \
--cc=mark.rutland@arm.com \
--cc=mingo@kernel.org \
--cc=namhyung@kernel.org \
--cc=peterz@infradead.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).