Re: [RFC PATCH v6 2/5] perf stat: Fork and launch perf record when perf stat needs to get retire latency value for a metric.

From: Namhyung Kim
Date: Tue Apr 23 2024 - 16:59:44 EST

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On Mon, Apr 1, 2024 at 2:23 PM Wang, Weilin <weilin.wang@xxxxxxxxx> wrote:
>
>
>
> > -----Original Message-----
> > From: Namhyung Kim <namhyung@xxxxxxxxxx>
> > Sent: Monday, April 1, 2024 1:58 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 v6 2/5] perf stat: Fork and launch perf record when
> > perf stat needs to get retire latency value for a metric.
> >
> > On Fri, Mar 29, 2024 at 12:12 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>
> > > ---
> > > tools/perf/builtin-stat.c | 190
> > +++++++++++++++++++++++++++++++++-
> > > tools/perf/util/data.c | 6 +-
> > > tools/perf/util/metricgroup.h | 8 ++
> > > tools/perf/util/stat.h | 2 +
> > > 4 files changed, 203 insertions(+), 3 deletions(-)
> > >
> > > diff --git a/tools/perf/builtin-stat.c b/tools/perf/builtin-stat.c
> > > index 6291e1e24535..7fbe47b0c44c 100644
> > > --- a/tools/perf/builtin-stat.c
> > > +++ b/tools/perf/builtin-stat.c
> > > @@ -94,8 +94,13 @@
> > > #include <perf/evlist.h>
> > > #include <internal/threadmap.h>
> > >
> > > +#include "util/sample.h"
> > > +#include <sys/param.h>
> > > +#include <subcmd/run-command.h>
> > > +
> > > #define DEFAULT_SEPARATOR " "
> > > #define FREEZE_ON_SMI_PATH "devices/cpu/freeze_on_smi"
> > > +#define PERF_DATA "-"
> > >
> > > static void print_counters(struct timespec *ts, int argc, const char **argv);
> > >
> > > @@ -163,6 +168,8 @@ static struct perf_stat_config stat_config = {
> > > .ctl_fd_ack = -1,
> > > .iostat_run = false,
> > > .tpebs_events = LIST_HEAD_INIT(stat_config.tpebs_events),
> > > + .tpebs_results = LIST_HEAD_INIT(stat_config.tpebs_results),
> > > + .tpebs_pid = -1,
> > > };
> > >
> > > static bool cpus_map_matched(struct evsel *a, struct evsel *b)
> > > @@ -684,15 +691,155 @@ static enum counter_recovery
> > stat_handle_error(struct evsel *counter)
> > >
> > > if (child_pid != -1)
> > > kill(child_pid, SIGTERM);
> > > + if (stat_config.tpebs_pid != -1)
> > > + kill(stat_config.tpebs_pid, SIGTERM);
> > > return COUNTER_FATAL;
> > > }
> > >
> > > -static int __run_perf_record(void)
> > > +static int __run_perf_record(const char **record_argv)
> > > {
> > > + int i = 0;
> > > + struct tpebs_event *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";
> > > +
> > > + 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_events, nd) {
> > > + record_argv[i++] = "-e";
> > > + record_argv[i++] = e->name;
> > > + }
> > > +
> > > + record_argv[i++] = "-o";
> > > + record_argv[i++] = PERF_DATA;
> > > +
> > > return 0;
> > > }
> >
> > Still I think it's weird it has 'perf record' in perf stat (despite the
> > 'perf stat record'). If it's only Intel thing and we don't have a plan
> > to do the same on other arches, we can move it to the arch
> > directory and keep the perf stat code simple.
>
> I'm not sure what is the proper way to solve this. And Ian mentioned
> that put code in arch directory could potentially cause other bugs.
> So I'm wondering if we could keep this code here for now. I could work
> on it later if we found it's better to be in arch directory.

Maybe somewhere in the util/ and keep the main code minimal.
IIUC it's only for very recent (or upcoming?) Intel CPUs and we
don't have tests (hopefully can run on other arch/CPUs).

So I don't think having it here would help fixing potential bugs.

> > >
> > > +static void prepare_run_command(struct child_process *cmd,
> > > + const char **argv)
> > > +{
> > > + memset(cmd, 0, sizeof(*cmd));
> > > + cmd->argv = argv;
> > > + cmd->out = -1;
> > > +}
> > > +
> > > +static int prepare_perf_record(struct child_process *cmd)
> > > +{
> > > + const char **record_argv;
> > > + int ret;
> > > +
> > > + record_argv = calloc(10 + 2 * stat_config.tpebs_event_size, sizeof(char
> > *));
> > > + if (!record_argv)
> > > + return -1;
> > > +
> > > + ret = __run_perf_record(record_argv);
> > > + if (ret)
> > > + return ret;
> > > +
> > > + prepare_run_command(cmd, record_argv);
> > > + return start_command(cmd);
> > > +}
> > > +
> > > +struct perf_script {
> > > + struct perf_tool tool;
> > > + struct perf_session *session;
> > > +};
> > > +
> > > +static void tpebs_data__delete(void)
> > > +{
> > > + struct tpebs_retire_lat *r, *rtmp;
> > > + struct tpebs_event *e, *etmp;
> > > +
> > > + list_for_each_entry_safe(r, rtmp, &stat_config.tpebs_results, event.nd)
> > {
> > > + list_del_init(&r->event.nd);
> > > + free(r);
> > > + }
> > > + list_for_each_entry_safe(e, etmp, &stat_config.tpebs_events, nd) {
> > > + list_del_init(&e->nd);
> > > + free(e);
> >
> > Shouldn't it free the names?
> >
> >
> > > + }
> > > +}
> > > +
> > > +static int process_sample_event(struct perf_tool *tool __maybe_unused,
> > > + union perf_event *event __maybe_unused,
> > > + struct perf_sample *sample,
> > > + struct evsel *evsel,
> > > + struct machine *machine __maybe_unused)
> > > +{
> > > + int ret = 0;
> > > + const char *evname;
> > > + struct tpebs_retire_lat *t;
> > > +
> > > + evname = evsel__name(evsel);
> > > +
> > > + /*
> > > + * Need to handle per core results? We are assuming average retire
> > > + * latency value will be used. Save the number of samples and the sum
> > of
> > > + * retire latency value for each event.
> > > + */
> > > + list_for_each_entry(t, &stat_config.tpebs_results, event.nd) {
> > > + if (!strcmp(evname, t->event.name)) {
> > > + t->count += 1;
> > > + t->sum += sample->retire_lat;
> > > + break;
> > > + }
> > > + }
> > > +
> > > + return ret;
> > > +}
> > > +
> > > +static int process_feature_event(struct perf_session *session,
> > > + union perf_event *event)
> > > +{
> > > + if (event->feat.feat_id < HEADER_LAST_FEATURE)
> > > + return perf_event__process_feature(session, event);
> > > + return 0;
> > > +}
> > > +
> > > +static void *__cmd_script(void *arg __maybe_unused)
> >
> > The arg is used.
> >
> > Also I don't like the name 'script' as it has nothing to do with
> > scripting. Maybe 'sample_reader', 'tpebs_reader' or
> > 'reader_thread'?
> >
> >
> > > +{
> > > + struct child_process *cmd = arg;
> > > + struct perf_session *session;
> > > + struct perf_data data = {
> > > + .mode = PERF_DATA_MODE_READ,
> > > + .path = PERF_DATA,
> > > + .file.fd = cmd->out,
> > > + };
> > > + struct perf_script script = {
> > > + .tool = {
> > > + .sample = process_sample_event,
> > > + .feature = process_feature_event,
> > > + .attr = perf_event__process_attr,
> >
> > Broken indentation. And if you just use the tool, you can
> > pass it directly.
> >
> >
> > > + },
> > > + };
> > > +
> > > + session = perf_session__new(&data, &script.tool);
> > > + if (IS_ERR(session))
> > > + return NULL;
> > > + script.session = session;
> > > + perf_session__process_events(session);
> > > + perf_session__delete(session);
> > > +
> > > + return NULL;
> > > +}
> > > +
> > > static int __run_perf_stat(int argc, const char **argv, int run_idx)
> > > {
> > > int interval = stat_config.interval;
> > > @@ -709,15 +856,38 @@ static int __run_perf_stat(int argc, const char
> > **argv, int run_idx)
> > > struct affinity saved_affinity, *affinity = NULL;
> > > int err;
> > > bool second_pass = false;
> > > + struct child_process cmd;
> > > + pthread_t thread_script;
> > >
> > > /* Prepare perf record for sampling event retire_latency before fork and
> > > * prepare workload */
> > > if (stat_config.tpebs_event_size > 0) {
> > > int ret;
> > > + struct tpebs_event *e;
> > >
> > > - ret = __run_perf_record();
> > > + pr_debug("perf stat pid = %d\n", getpid());
> > > + list_for_each_entry(e, &stat_config.tpebs_events, nd) {
> > > + struct tpebs_retire_lat *new = malloc(sizeof(struct
> > tpebs_retire_lat));
> > > +
> > > + if (!new)
> > > + return -1;
> > > + new->event.name = strdup(e->name);
> > > + new->event.tpebs_name = strdup(e->tpebs_name);
> >
> > These can fail too.
> >
> >
> > > + new->count = 0;
> > > + new->sum = 0;
> > > + list_add_tail(&new->event.nd, &stat_config.tpebs_results);
> > > + }
> > > + ret = prepare_perf_record(&cmd);
> > > if (ret)
> > > return ret;
> > > + if (pthread_create(&thread_script, NULL, __cmd_script, &cmd)) {
> > > + kill(cmd.pid, SIGTERM);
> > > + close(cmd.out);
> > > + pr_err("Could not create thread to process sample data.\n");
> > > + return -1;
> > > + }
> > > + /* Wait for perf record initialization a little bit.*/
> > > + sleep(2);
> >
> > This won't guarantee anything. If you want to make sure the
> > 'thread_script' to run before the 'perf record' process, you can
> > use a pipe to signal that like in evlist__prepare_workload() and
> > evlist__start_workload().
>
> This sleep is added to make perf stat wait for record initialization because in the
> case that the workload runs very small a mount of time, we'd like to ensure perf
> record has enough time to launch and start collecting sample data.

But waiting for 2 seconds won't solve the problem.

>
> Because the code uses the common API in run-command.h to do the fork, I think
> it cannot use PIPE like in evlist__prepare_workload to sync and start perf record
> and perf stat data collection together. Please correct me if I'm wrong here.

Ok, it'd be hard to sync both perf record and perf stat with a single workload.
I think you can try --control option in perf record to enable/disable
with timing
you want. Also --synth=no should reduce a lot of overhead during
initialization.
Maybe you can also add --synth=no-kernel to completely skip the synthesis.

Thanks,
Namhyung

> > > }
> > >
> > > if (forks) {
> > > @@ -925,6 +1095,17 @@ static int __run_perf_stat(int argc, const char
> > **argv, int run_idx)
> > >
> > > t1 = rdclock();
> > >
> > > + if (stat_config.tpebs_event_size > 0) {
> > > + int ret;
> > > +
> > > + kill(cmd.pid, SIGTERM);
> > > + pthread_join(thread_script, NULL);
> > > + close(cmd.out);
> > > + ret = finish_command(&cmd);
> > > + if (ret != -ERR_RUN_COMMAND_WAITPID_SIGNAL)
> > > + return ret;
> > > + }
> > > +
> > > if (stat_config.walltime_run_table)
> > > stat_config.walltime_run[run_idx] = t1 - t0;
> > >
> > > @@ -1032,6 +1213,9 @@ static void sig_atexit(void)
> > > if (child_pid != -1)
> > > kill(child_pid, SIGTERM);
> > >
> > > + if (stat_config.tpebs_pid != -1)
> > > + kill(stat_config.tpebs_pid, SIGTERM);
> > > +
> > > sigprocmask(SIG_SETMASK, &oset, NULL);
> > >
> > > if (signr == -1)
> > > @@ -2972,5 +3156,7 @@ int cmd_stat(int argc, const char **argv)
> > > metricgroup__rblist_exit(&stat_config.metric_events);
> > > evlist__close_control(stat_config.ctl_fd, stat_config.ctl_fd_ack,
> > &stat_config.ctl_fd_close);
> > >
> > > + tpebs_data__delete();
> > > +
> > > return status;
> > > }
> > > diff --git a/tools/perf/util/data.c b/tools/perf/util/data.c
> > > index 08c4bfbd817f..98e3014c0aef 100644
> > > --- a/tools/perf/util/data.c
> > > +++ b/tools/perf/util/data.c
> > > @@ -204,7 +204,11 @@ static bool check_pipe(struct perf_data *data)
> > > data->file.fd = fd;
> > > data->use_stdio = false;
> > > }
> > > - } else {
> > > + /*
> > > + * When is_pipe and data->file.fd is given, use given fd
> > > + * instead of STDIN_FILENO or STDOUT_FILENO
> > > + */
> > > + } else if (data->file.fd <= 0) {
> > > data->file.fd = fd;
> > > }
> > > }
> >
> > I think this can be in a separate commit.
> >
> >
> > > diff --git a/tools/perf/util/metricgroup.h b/tools/perf/util/metricgroup.h
> > > index 7c24ed768ff3..ae788edef30f 100644
> > > --- a/tools/perf/util/metricgroup.h
> > > +++ b/tools/perf/util/metricgroup.h
> > > @@ -68,10 +68,18 @@ struct metric_expr {
> > >
> > > struct tpebs_event {
> > > struct list_head nd;
> > > + /* Event name */
> > > const char *name;
> > > + /* Event name with the TPEBS modifier R */
> > > const char *tpebs_name;
> > > };
> > >
> > > +struct tpebs_retire_lat {
> > > + struct tpebs_event event;
> > > + size_t count;
> > > + int sum;
> > > +};
> >
> > Actually I don't know why you need this separate structure.
> > Can we just use tpebs_event?
>
> Currently, we use average value as the retire latency value in metrics. But we
> might update it to use other value, for example the minimum or maximum. So, I thought
> it would be better to have a dedicated data structure to handle this data I could update
> the code to use tpebs_event if you still feel that's better.
>
> Thanks,
> Weilin
>
> >
> > Thanks,
> > Namhyung
> >
> >
> > > +
> > > struct metric_event *metricgroup__lookup(struct rblist *metric_events,
> > > struct evsel *evsel,
> > > bool create);
> > > diff --git a/tools/perf/util/stat.h b/tools/perf/util/stat.h
> > > index b987960df3c5..0726bdc06681 100644
> > > --- a/tools/perf/util/stat.h
> > > +++ b/tools/perf/util/stat.h
> > > @@ -111,6 +111,8 @@ struct perf_stat_config {
> > > struct rblist metric_events;
> > > struct list_head tpebs_events;
> > > size_t tpebs_event_size;
> > > + struct list_head tpebs_results;
> > > + pid_t tpebs_pid;
> > > int ctl_fd;
> > > int ctl_fd_ack;
> > > bool ctl_fd_close;
> > > --
> > > 2.43.0
> > >

Next message: Andy Shevchenko: "[PATCH v1 1/1] fs/ntfs3: Drop stray '\' (backslash) in formatting string"
Previous message: kernel test robot: "Re: [PATCH 2/4] memcg: reduce memory for the lruvec and memcg stats"
Next in thread: Wang, Weilin: "RE: [RFC PATCH v6 2/5] perf stat: Fork and launch perf record when perf stat needs to get retire latency value for a metric."
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