From: "nakamura.shun@fujitsu.com" <nakamura.shun@fujitsu.com>
To: Jiri Olsa <jolsa@redhat.com>
Cc: Rob Herring <robh@kernel.org>,
"peterz@infradead.org" <peterz@infradead.org>,
"mingo@redhat.com" <mingo@redhat.com>,
"acme@kernel.org" <acme@kernel.org>,
"mark.rutland@arm.com" <mark.rutland@arm.com>,
"alexander.shishkin@linux.intel.com"
<alexander.shishkin@linux.intel.com>,
"namhyung@kernel.org" <namhyung@kernel.org>,
"irogers@google.com" <irogers@google.com>,
"linux-perf-users@vger.kernel.org"
<linux-perf-users@vger.kernel.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v2 1/2] libperf: Add processing to scale the counters obtained during the read() system call when multiplexing
Date: Mon, 8 Nov 2021 00:49:24 +0000 [thread overview]
Message-ID: <OSBPR01MB4600CC928A1D4BB0703EFAE3F7919@OSBPR01MB4600.jpnprd01.prod.outlook.com> (raw)
In-Reply-To: <OSBPR01MB46000071426DEC8FFF04C4F6F7BD9@OSBPR01MB4600.jpnprd01.prod.outlook.com>
Hi Jirka
> > > > On Wed, Sep 22, 2021 at 07:16:26PM +0900, Shunsuke Nakamura wrote:
> > > > > From: nakamura shunsuke <nakamura.shun@fujitsu.com>
> > > > >
> > > > > perf_evsel__read() scales counters obtained by RDPMC during multiplexing, but
> > > > > does not scale counters obtained by read() system call.
> > > > >
> > > > > Add processing to perf_evsel__read() to scale the counters obtained during the
> > > > > read() system call when multiplexing.
> > > > >
> > > > >
> > > > > Signed-off-by: Shunsuke Nakamura <nakamura.shun@fujitsu.com>
> > > > > ---
> > > > > tools/lib/perf/evsel.c | 6 ++++++
> > > > > 1 file changed, 6 insertions(+)
> > > > >
> > > > > diff --git a/tools/lib/perf/evsel.c b/tools/lib/perf/evsel.c
> > > > > index 8441e3e1aaac..0ebd1d34436f 100644
> > > > > --- a/tools/lib/perf/evsel.c
> > > > +++ b/tools/lib/perf/evsel.c
> > > > > @@ -18,6 +18,7 @@
> > > > > #include <sys/ioctl.h>
> > > > > #include <sys/mman.h>
> > > > > #include <asm/bug.h>
> > > > > +#include <linux/math64.h>
> > > > >
> > > > > void perf_evsel__init(struct perf_evsel *evsel, struct perf_event_attr *attr,
> > > > > int idx)
> > > > > @@ -321,6 +322,11 @@ int perf_evsel__read(struct perf_evsel *evsel, int cpu, int thread,
> > > > > if (readn(*fd, count->values, size) <= 0)
> > > > > return -errno;
> > > > >
> > > > > + if (count->ena != count->run) {
> > > > > + if (count->run != 0)
> > > > > + count->val = mul_u64_u64_div64(count->val, count->ena, count->run);
> > > > > + }
> > > >
> > > > so I think perf stat expect raw values in there and does the
> > > > scaling by itself, please check following code:
> > > >
> > > > read_counters
> > > > read_affinity_counters
> > > > read_counter_cpu
> > > > read_single_counter
> > > > evsel__read_counter
> > > >
> > > > perf_stat_process_counter
> > > > process_counter_maps
> > > > process_counter_values
> > > > perf_counts_values__scale
> > > >
> > > >
> > > > perhaps we could export perf_counts_values__scale if it'd be any help
> > >
> > > Thank you for your comment.
> > >
> > > The purpose of this patch is to unify the counters obtained with
> > > perf_evsel__read() to scaled or unscaled values.
> > >
> > > perf_evsel__read() gets counter by perf_mmap__read_self() if RDPMC is
> > > available, else gets by readn(). In current implementation, caller
> > > gets scaled counter if goes through RDPMC path, otherwise gets unscaled
> > > counter via readn() path.
> > >
> > > However caller cannnot know which path were taken.
> > >
> > > If caller expects a raw value, I think the RDPMC path should also
> > > return an unscaled counter.
> > >
> > > diff --git a/tools/lib/perf/mmap.c b/tools/lib/perf/mmap.c
> > > index c89dfa5..aaa4579 100644
> > > --- a/tools/lib/perf/mmap.c
> > > +++ b/tools/lib/perf/mmap.c
> > > @@ -353,8 +353,6 @@ int perf_mmap__read_self(struct perf_mmap *map, struct perf_counts_values *count
> > > count->ena += delta;
> > > if (idx)
> > > count->run += delta;
> > > -
> > > - cnt = mul_u64_u64_div64(cnt, count->ena, count->run);
> >
> > perf stat does not mmap counters so this should not be invoked
> > within perf stat.. but we should be consistent and scale after
> > calling perf_evsel__read.. and give user the possibility to get
> > un-scaled counts
> >
> > that perhaps brings new feature.. mmap perf stat counters to invoke
> > the fast reading path for counters.. IIRC it should be matter just
> > to mmap the first 'user' page
>
> Thank you for your comment.
> I think it will be good that perf stat supports rdpmc.
>
> I will modify the patch.
I think rdpmc cannot measure the command/program specified in perf stat
because it measures the calling thread of perf_event_open.
If my understanding is wrong, please point it out to me.
Best Regards
Shunsuke
next prev parent reply other threads:[~2021-11-08 0:50 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-09-22 10:16 [PATCH v2 0/2] libperf: Add support for scaling counters obtained from the read() system call during multiplexing Shunsuke Nakamura
2021-09-22 10:16 ` [PATCH v2 1/2] libperf: Add processing to scale the counters obtained during the read() system call when multiplexing Shunsuke Nakamura
2021-09-22 21:34 ` Jiri Olsa
2021-09-28 9:53 ` nakamura.shun
2021-10-05 16:36 ` Rob Herring
2021-10-19 4:59 ` nakamura.shun
2021-10-07 17:17 ` Jiri Olsa
2021-10-19 5:00 ` nakamura.shun
2021-11-08 0:49 ` nakamura.shun [this message]
2021-11-14 16:16 ` Jiri Olsa
2021-09-22 10:16 ` [PATCH v2 2/2] libperf tests: Add test_stat_multiplexing test Shunsuke Nakamura
2021-10-08 19:11 ` Arnaldo Carvalho de Melo
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