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Mon, 20 Jan 2020 09:29:33 +0000 (UTC) Received: from krava (unknown [10.43.17.48]) by smtp.corp.redhat.com (Postfix) with ESMTPS id B25A360C05; Mon, 20 Jan 2020 09:29:30 +0000 (UTC) Date: Mon, 20 Jan 2020 10:29:28 +0100 From: Jiri Olsa To: Kim Phillips Cc: Arnaldo Carvalho de Melo , Peter Zijlstra , Ingo Molnar , Mark Rutland , Alexander Shishkin , Jiri Olsa , Namhyung Kim , Cong Wang , Andi Kleen , Jin Yao , Kan Liang , Song Liu , Davidlohr Bueso , linux-perf-users@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 2/2] perf stat: don't report a null stalled cycles per insn metric Message-ID: <20200120092928.GD608405@krava> References: <20200115222949.7247-1-kim.phillips@amd.com> <20200115222949.7247-2-kim.phillips@amd.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200115222949.7247-2-kim.phillips@amd.com> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Jan 15, 2020 at 04:29:49PM -0600, Kim Phillips wrote: > For data collected on machines with front end stalled cycles supported, > such as found on modern AMD CPU families, commit 146540fb545b ("perf > stat: Always separate stalled cycles per insn") introduces a new line > in CSV output with a leading comma that upsets some automated scripts. > Scripts have to use "-e ex_ret_instr" to work around this issue, after > upgrading to a version of perf with that commit. > > We could add "if (have_frontend_stalled && !config->csv_sep)" > to the not (total && avg) else clause, to emphasize that CSV users > are usually scripts, and are written to do only what is needed, i.e., > they wouldn't typically invoke "perf stat" without specifying an > explicit event list. > > But - let alone CSV output - why should users now tolerate a constant > 0-reporting extra line in regular terminal output?: > > BEFORE: > > $ sudo perf stat --all-cpus -einstructions,cycles -- sleep 1 > > Performance counter stats for 'system wide': > > 181,110,981 instructions # 0.58 insn per cycle > # 0.00 stalled cycles per insn > 309,876,469 cycles > > 1.002202582 seconds time elapsed > > The user would not like to see the now permanent > "0.00 stalled cycles per insn" line fixture, as it gives > no useful information. > > So this patch removes the printing of the zeroed stalled cycles > line altogether, almost reverting the very original commit fb4605ba47e7 > ("perf stat: Check for frontend stalled for metrics"), which seems > like it was written to normalize --metric-only column output > of common Intel machines at the time: modern Intel machines > have ceased to support the genericised frontend stalled metrics AFAICT. > > AFTER: > > $ sudo perf stat --all-cpus -einstructions,cycles -- sleep 1 > > Performance counter stats for 'system wide': > > 244,071,432 instructions # 0.69 insn per cycle > 355,353,490 cycles > > 1.001862516 seconds time elapsed > > Output behaviour when stalled cycles is indeed measured is not affected > (BEFORE == AFTER): > > $ sudo perf stat --all-cpus -einstructions,cycles,stalled-cycles-frontend -- sleep 1 > > Performance counter stats for 'system wide': > > 247,227,799 instructions # 0.63 insn per cycle > # 0.26 stalled cycles per insn > 394,745,636 cycles > 63,194,485 stalled-cycles-frontend # 16.01% frontend cycles idle > > 1.002079770 seconds time elapsed looks reasonable to me, Andi, are you ok with this? Acked-by: Jiri Olsa > Cc: Peter Zijlstra > Cc: Ingo Molnar > Cc: Arnaldo Carvalho de Melo > Cc: Mark Rutland > Cc: Alexander Shishkin > Cc: Jiri Olsa > Cc: Namhyung Kim > Cc: Cong Wang > Cc: Andi Kleen > Cc: Jin Yao > Cc: Kan Liang > Cc: Kim Phillips > Cc: Song Liu > Cc: Davidlohr Bueso > Cc: linux-perf-users@vger.kernel.org > Cc: linux-kernel@vger.kernel.org > Fixes: 146540fb545b ("perf stat: Always separate stalled cycles per insn") > Signed-off-by: Kim Phillips > --- > tools/perf/util/stat-shadow.c | 6 ------ > 1 file changed, 6 deletions(-) > > diff --git a/tools/perf/util/stat-shadow.c b/tools/perf/util/stat-shadow.c > index 2c41d47f6f83..90d23cc3c8d4 100644 > --- a/tools/perf/util/stat-shadow.c > +++ b/tools/perf/util/stat-shadow.c > @@ -18,7 +18,6 @@ > * AGGR_NONE: Use matching CPU > * AGGR_THREAD: Not supported? > */ > -static bool have_frontend_stalled; > > struct runtime_stat rt_stat; > struct stats walltime_nsecs_stats; > @@ -144,7 +143,6 @@ void runtime_stat__exit(struct runtime_stat *st) > > void perf_stat__init_shadow_stats(void) > { > - have_frontend_stalled = pmu_have_event("cpu", "stalled-cycles-frontend"); > runtime_stat__init(&rt_stat); > } > > @@ -853,10 +851,6 @@ void perf_stat__print_shadow_stats(struct perf_stat_config *config, > print_metric(config, ctxp, NULL, "%7.2f ", > "stalled cycles per insn", > ratio); > - } else if (have_frontend_stalled) { > - out->new_line(config, ctxp); > - print_metric(config, ctxp, NULL, "%7.2f ", > - "stalled cycles per insn", 0); > } > } else if (perf_evsel__match(evsel, HARDWARE, HW_BRANCH_MISSES)) { > if (runtime_stat_n(st, STAT_BRANCHES, ctx, cpu) != 0) > -- > 2.24.1 >