linux-kernel - 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.

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Date: Fri, 17 May 2024 14:43:08 -0700
From: Namhyung Kim <namhyung@...nel.org>
To: weilin.wang@...el.com
Cc: Ian Rogers <irogers@...gle.com>, Arnaldo Carvalho de Melo <acme@...nel.org>, 
	Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>, 
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>, Jiri Olsa <jolsa@...nel.org>, 
	Adrian Hunter <adrian.hunter@...el.com>, Kan Liang <kan.liang@...ux.intel.com>, 
	linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org, 
	Perry Taylor <perry.taylor@...el.com>, Samantha Alt <samantha.alt@...el.com>, 
	Caleb Biggers <caleb.biggers@...el.com>
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@...el.com> wrote:
>
> From: Weilin Wang <weilin.wang@...el.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.
>
> 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@...el.com>
> Reviewed-by: Ian Rogers <irogers@...gle.com>
> ---
[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.

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;
> +}
> +
>