RE: [RFC PATCH v8 3/7] perf stat: Fork and launch perf record when perf stat needs to get retire latency value for a metric.

[Wang, Weilin]

> -----Original Message-----
> From: Namhyung Kim <namhyung@xxxxxxxxxx>
> Sent: Friday, May 17, 2024 2:43 PM
> To: Wang, Weilin <weilin.wang@xxxxxxxxx>
> Cc: Ian Rogers <irogers@xxxxxxxxxx>; Arnaldo Carvalho de Melo
> <acme@xxxxxxxxxx>; Peter Zijlstra <peterz@xxxxxxxxxxxxx>; Ingo Molnar
> <mingo@xxxxxxxxxx>; Alexander Shishkin
> <alexander.shishkin@xxxxxxxxxxxxxxx>; Jiri Olsa <jolsa@xxxxxxxxxx>; Hunter,
> Adrian <adrian.hunter@xxxxxxxxx>; Kan Liang <kan.liang@xxxxxxxxxxxxxxx>;
> linux-perf-users@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; Taylor, Perry
> <perry.taylor@xxxxxxxxx>; Alt, Samantha <samantha.alt@xxxxxxxxx>; Biggers,
> Caleb <caleb.biggers@xxxxxxxxx>
> Subject: Re: [RFC PATCH v8 3/7] perf stat: Fork and launch perf record when
> perf stat needs to get retire latency value for a metric.
> 
> On Tue, May 14, 2024 at 10:44 PM <weilin.wang@xxxxxxxxx> wrote:
> >
> > From: Weilin Wang <weilin.wang@xxxxxxxxx>
> >
> > 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.
> >
> > At the point of time that perf stat stops counting, it would send sigterm
> signal
> > to perf record process and receiving sampling data back from perf record
> from a
> > pipe. Perf stat will then process the received data to get retire latency data
> > and calculate metric result.
> >
> > Another thread is required to synchronize between perf stat and perf record
> > when we pass data through pipe.
> >
> > Signed-off-by: Weilin Wang <weilin.wang@xxxxxxxxx>
> > Reviewed-by: Ian Rogers <irogers@xxxxxxxxxx>
> > ---
> [SNIP]
> > diff --git a/tools/perf/util/intel-tpebs.c b/tools/perf/util/intel-tpebs.c
> > new file mode 100644
> > index 000000000000..4b7a98794fae
> > --- /dev/null
> > +++ b/tools/perf/util/intel-tpebs.c
> > @@ -0,0 +1,285 @@
> > +// SPDX-License-Identifier: GPL-2.0-only
> > +/*
> > + * intel_pt.c: Intel Processor Trace support
> > + * Copyright (c) 2013-2015, Intel Corporation.
> 
> This needs some updates. :)
> 
> 
> > + */
> > +
> > +
> > +#include <sys/param.h>
> > +#include <subcmd/run-command.h>
> > +#include <thread.h>
> > +#include "intel-tpebs.h"
> > +#include <linux/list.h>
> > +#include <linux/zalloc.h>
> > +#include <linux/err.h>
> > +#include "sample.h"
> > +#include "debug.h"
> > +#include "evlist.h"
> > +#include "evsel.h"
> > +#include "session.h"
> > +#include "tool.h"
> > +#include "metricgroup.h"
> > +#include <sys/stat.h>
> > +#include <sys/file.h>
> > +
> > +
> > +
> > +#define PERF_DATA              "-"
> > +#define CONTROL                        "/tmp/control"
> > +#define ACK                    "/tmp/ack"
> > +pthread_t reader_thread;
> > +struct child_process *cmd;
> > +struct perf_stat_config *stat_config;
> 
> static ?
> 
> > +
> > +static int get_perf_record_args(const char **record_argv)
> > +{
> > +       int i = 0;
> > +       struct tpebs_retire_lat *e;
> > +
> > +       pr_debug("Prepare perf record for retire_latency\n");
> > +
> > +       record_argv[i++] = "perf";
> > +       record_argv[i++] = "record";
> > +       record_argv[i++] = "-W";
> > +       record_argv[i++] = "--synth=no";
> 
> Unfortunately this still synthesizes MMAP records for the kernel
> and modules.  As we don't care about them and just want to
> minimize the overhead at the beginning, we can add
> "--tail-synthesize" too.
> 
> 
> > +       record_argv[i++] = "--control=fifo:/tmp/control,/tmp/ack";
> 
> This hard-coded path won't work well when more than one users
> want to run the perf command at the same time.
> 
Hi Namhyung,

Yes, this is not a good implementation. I'm going to update this named 
pipe and all the related code. 


Thanks,
Weilin

> Thanks,
> Namhyung
> 
> > +
> > +       if (stat_config->user_requested_cpu_list) {
> > +               record_argv[i++] = "-C";
> > +               record_argv[i++] = stat_config->user_requested_cpu_list;
> > +       }
> > +
> > +       if (stat_config->system_wide)
> > +               record_argv[i++] = "-a";
> > +
> > +       if (!stat_config->system_wide && !stat_config-
> >user_requested_cpu_list) {
> > +               pr_err("Require -a or -C option to run sampling.\n");
> > +               return -ECANCELED;
> > +       }
> > +
> > +       list_for_each_entry(e, &stat_config->tpebs_results, nd) {
> > +               record_argv[i++] = "-e";
> > +               record_argv[i++] = e->name;
> > +       }
> > +
> > +       record_argv[i++] = "-o";
> > +       record_argv[i++] = PERF_DATA;
> > +
> > +       return 0;
> > +}
> > +
> >