linux-kernel - Re: [PATCH 2/2] perf tests: add test for trace output loss

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Message-ID: <ZzZlpwTy_nXKE8LF@x1>
Date: Thu, 14 Nov 2024 18:03:35 -0300
From: Arnaldo Carvalho de Melo <acme@...nel.org>
To: Howard Chu <howardchu95@...il.com>
Cc: Benjamin Peterson <benjamin@...flow.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>, Namhyung Kim <namhyung@...nel.org>,
	Mark Rutland <mark.rutland@....com>,
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
	Jiri Olsa <jolsa@...nel.org>, Ian Rogers <irogers@...gle.com>,
	Adrian Hunter <adrian.hunter@...el.com>,
	"Liang, Kan" <kan.liang@...ux.intel.com>,
	open list <linux-kernel@...r.kernel.org>,
	"open list:PERFORMANCE EVENTS SUBSYSTEM" <linux-perf-users@...r.kernel.org>
Subject: Re: [PATCH 2/2] perf tests: add test for trace output loss

On Thu, Nov 14, 2024 at 12:16:46PM -0800, Howard Chu wrote:
> Hello,
> 
> On Thu, Nov 14, 2024 at 12:09 PM Arnaldo Carvalho de Melo
> <acme@...nel.org> wrote:
> >
> > On Thu, Nov 14, 2024 at 09:44:56AM -0800, Benjamin Peterson wrote:
> > > > On Thu, Nov 14, 2024 at 02:37:52PM -0300, Arnaldo Carvalho de Melo wrote:
> > > > diff --git a/tools/perf/tests/shell/trace_exit_race.sh b/tools/perf/tests/shell/trace_exit_race.sh
> > > > index 8b70324bc5b4fb4c..c37ed6bb9f7e8fab 100755
> > > > --- a/tools/perf/tests/shell/trace_exit_race.sh
> > > > +++ b/tools/perf/tests/shell/trace_exit_race.sh
> > > > @@ -12,10 +12,10 @@
> > > >  skip_if_no_perf_trace || exit 2
> >
> > > >  trace_shutdown_race() {
> > > > -       for i in $(seq 100); do
> > > > +       for _ in $(seq 100); do
> > > >                 perf trace -e syscalls:sys_enter_exit_group true 2>>$file
> > > >         done
> > > > -       [ $(grep -c -E " +[0-9]+\.[0-9]+ +true/[0-9]+ syscalls:sys_enter_exit_group\(\)$" $file) = "100" ]
> > > > +       [ "$(grep -c -E ' +[0-9]+\.[0-9]+ +true/[0-9]+ syscalls:sys_enter_exit_group\(\)$' $file)" = "100" ]
> > > >  }
> >
> > > This all looks okay.
> >
> > The test is failing for me as there is garbage in the output of perf
> > trace even with Namhyung having already applied your previous patch:
> >
> > ⬢ [acme@...lbox perf-tools-next]$ git log --oneline --author benjamin@...flow.com
> > 12bd434f68ea45c7 (HEAD -> perf-tools-next) perf tests: Add test for 'perf trace' output loss
> > efbcd2cd7eac10a9 perf trace: Do not lose last events in a race
> > 5fb8e56542a3cf46 (perf-tools-next/tmp.perf-tools-next) perf trace: avoid garbage when not printing a trace event's arguments
> > ⬢ [acme@...lbox perf-tools-next]$
> >
> > root@...ber:~# perf trace -e syscalls:sys_enter_exit_group true
> >      0.000 true/1982428 syscalls:sys_enter_exit_group( k?m)
> > root@...ber:~# perf trace -e syscalls:sys_enter_exit_group true
> >      0.000 true/1982430 syscalls:sys_enter_exit_group()
> > root@...ber:~# perf trace -e syscalls:sys_enter_exit_group true
> >      0.000 true/1982432 syscalls:sys_enter_exit_group()
> > root@...ber:~# perf trace -e syscalls:sys_enter_exit_group true
> >      0.000 true/1982434 syscalls:sys_enter_exit_group()
> > root@...ber:~# perf trace -e syscalls:sys_enter_exit_group true
> >      0.000 true/1982437 syscalls:sys_enter_exit_group( k�)
> > root@...ber:~# perf trace -e syscalls:sys_enter_exit_group true
> >      0.000 true/1982439 syscalls:sys_enter_exit_group(, loads 8��1)
> > root@...ber:~#
> >
> > So we don't _miss_ the events, which I was noticing and brought me to
> > test your latest 2 patches, which I applied and added a Tested-by, now
> > tryint to figure out this garbage...
> 
> Benjamin has already sent v2 to fix this:
> https://lore.kernel.org/linux-perf-users/20241107232128.108981-2-benjamin@engflow.com/

Interesting, I wonder why b4 didn't pick the v2 :-\

I'll try it, but see my other message, maybe the way I fixed is simpler?
Its a two liner that could be turned into a one liner by right at the
start of the function setting bf[0] = '\0', that way we wouldn't need
even to check if printed == 0 at the end.

Anyway, will test the newer version.

- Arnaldo