Messages in this thread | | | From | "Wang, Weilin" <> | Subject | RE: [RFC PATCH v4 2/6] perf stat: Fork and launch perf record when perf stat needs to get retire latency value for a metric. | Date | Wed, 13 Mar 2024 00:26:26 +0000 |
| |
> -----Original Message----- > From: Andi Kleen <ak@linux.intel.com> > Sent: Tuesday, March 12, 2024 5:03 PM > To: Wang, Weilin <weilin.wang@intel.com> > Cc: Namhyung Kim <namhyung@kernel.org>; Ian Rogers > <irogers@google.com>; Arnaldo Carvalho de Melo <acme@kernel.org>; Peter > Zijlstra <peterz@infradead.org>; Ingo Molnar <mingo@redhat.com>; > Alexander Shishkin <alexander.shishkin@linux.intel.com>; Jiri Olsa > <jolsa@kernel.org>; Hunter, Adrian <adrian.hunter@intel.com>; Kan Liang > <kan.liang@linux.intel.com>; linux-perf-users@vger.kernel.org; linux- > kernel@vger.kernel.org; Taylor, Perry <perry.taylor@intel.com>; Alt, Samantha > <samantha.alt@intel.com>; Biggers, Caleb <caleb.biggers@intel.com> > Subject: Re: [RFC PATCH v4 2/6] perf stat: Fork and launch perf record when > perf stat needs to get retire latency value for a metric. > > weilin.wang@intel.com writes: > > > From: Weilin Wang <weilin.wang@intel.com> > > > > When retire_latency value is used in a metric formula, perf stat would fork a > > perf record process with "-e" and "-W" options. Perf record will collect > > required retire_latency values in parallel while perf stat is collecting > > counting values. > > How does that work when the workload is specified on the command line? > The workload would run twice? That is very inefficient and may not > work if it's a large workload. > > The perf tool infrastructure is imho not up to the task of such > parallel collection. > > Also it won't work for very long collections because you will get a > very large perf.data. Better to use a pipeline. > > I think it would be better if you made it a separate operation that can > generate a file that is then consumed by perf stat. This is also more efficient > because often the calibration is only needed once. And it's all under > user control so no nasty surprises. >
Workload runs only once with perf stat. Perf record is forked by perf stat and run in parallel with perf stat. Perf stat will send perf record a signal to terminate after perf stat stops collecting count value.
The implementation uses a PIPE to pass the sampled data from perf record instead of writing the data into a file.
Thanks, Weilin
> -Andi
| |