From: Peter Zijlstra <peterz@infradead.org>
To: Namhyung Kim <namhyung@kernel.org>
Cc: Jiri Olsa <jolsa@redhat.com>, 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>,
Stephane Eranian <eranian@google.com>,
Andi Kleen <ak@linux.intel.com>, Ian Rogers <irogers@google.com>,
Gabriel Marin <gmx@google.com>
Subject: Re: [RFC] perf/core: Add an ioctl to get a number of lost samples
Date: Tue, 24 Aug 2021 16:02:18 +0200 [thread overview]
Message-ID: <YST76vy8UQRCaKtO@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <CAM9d7ci2ZkJ-FK0R1VoYjZZ9GzB4qDrPY=JD6_eOyUFQ1DLh7Q@mail.gmail.com>
On Wed, Aug 11, 2021 at 01:54:09PM -0700, Namhyung Kim wrote:
> Hi Jiri,
>
> 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
>
> Oh, right... I forgot about that, sorry.
> But I think the lost count is not collected accurately.
>
> Peter, what do you think about the interface (read vs ioctl)?
I think I'm the one that suggested PERF_FORMAT_LOST at the time :-)
next prev parent reply other threads:[~2021-08-24 14:05 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
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 [this message]
2021-08-24 17:55 ` Namhyung Kim
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