linux-kernel - Re: [PATCH 2/2] perf stat: fix unexpected delay behaviour

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Date:   Wed, 14 Dec 2022 14:35:01 -0300
From:   Arnaldo Carvalho de Melo <acme@...nel.org>
To:     Leo Yan <leo.yan@...aro.org>
Cc:     Namhyung Kim <namhyung@...nel.org>,
        James Clark <james.clark@....com>,
        Adrián Herrera Arcila 
        <adrian.herrera@....com>, linux-kernel@...r.kernel.org,
        linux-perf-users@...r.kernel.org, songliubraving@...com,
        peterz@...radead.org, mingo@...hat.com, mark.rutland@....com,
        alexander.shishkin@...ux.intel.com, jolsa@...nel.org
Subject: Re: [PATCH 2/2] perf stat: fix unexpected delay behaviour

Em Wed, Dec 14, 2022 at 11:57:21PM +0800, Leo Yan escreveu:
> On Wed, Dec 14, 2022 at 11:41:55AM -0300, Arnaldo Carvalho de Melo wrote:
> > Em Tue, Dec 13, 2022 at 08:40:31AM -0800, Namhyung Kim escreveu:
> > > Hi,
> > > 
> > > On Tue, Dec 13, 2022 at 6:44 AM Arnaldo Carvalho de Melo
> > > <acme@...nel.org> wrote:
> > > >
> > > > Em Mon, Aug 01, 2022 at 09:20:37AM +0100, James Clark escreveu:
> > > > >
> > > > >
> > > > > On 29/07/2022 17:12, Adrián Herrera Arcila wrote:
> > > > > > The described --delay behaviour is to delay the enablement of events, but
> > > > > > not the execution of the command, if one is passed, which is incorrectly
> > > > > > the current behaviour.
> > > > > >
> > > > > > This patch decouples the enablement from the delay, and enables events
> > > > > > before or after launching the workload dependent on the options passed
> > > > > > by the user. This code structure is inspired by that in perf-record, and
> > > > > > tries to be consistent with it.
> > > > > >
> > > > > > Link: https://lore.kernel.org/linux-perf-users/7BFD066E-B0A8-49D4-B635-379328F0CF4C@fb.com
> > > > > > Fixes: d0a0a511493d ("perf stat: Fix forked applications enablement of counters")
> > > > > > Signed-off-by: Adrián Herrera Arcila <adrian.herrera@....com>
> > > > > > ---
> > > > > >  tools/perf/builtin-stat.c | 56 ++++++++++++++++++++++-----------------
> > > > > >  1 file changed, 32 insertions(+), 24 deletions(-)
> > > > >
> > > > > Looks good to me. Fixes the counter delay issue and the code is pretty
> > > > > similar to perf record now. Although I would wait for Leo's or Song's
> > > > > comment as well because they were involved.
> > > >
> > > > I think I didn't notice Leo's ack, it still applies, so I'm doing it
> > > > now.
> > > 
> > > I think the BPF counters should be enabled/disabled together.
> > 
> > Ok, so I removed this one and applied Namhyung's.
> 
> I can guess why Adrián doesn't enable/disable BPF counters together :)
> 
> Since 'perf stat' doesn't enable BPF counters with other normal PMU
> events in the first place, I believe this is deliberately by Song's
> patch fa853c4b839e ("perf stat: Enable counting events for BPF
> programs"), it says:
> 
> "'perf stat -b' creates per-cpu perf_event and loads fentry/fexit BPF
> programs (monitor-progs) to the target BPF program (target-prog). The
> monitor-progs read perf_event before and after the target-prog, and
> aggregate the difference in a BPF map. Then the user space reads data
> from these maps".
> 
> IIUC, when loading eBPF (counter) program, perf tool needs to handle
> eBPF program map specially (so that perf tool can know the latest eBPF
> program's map in kernel).
> 
> I don't know anything for eBPF counter, so this is why I am still a bit
> puzzle which way is right to do (bind vs separate eBPF counters).  But
> I personally prefer to let eBPF counter to respect delay, so it's fine
> for me to apply Namhyung's patch.

"I'm fine" can be read as an Acked-by, right? :-)

- Arnaldo