Re: [RFC PATCH v2 1/3] perf evsel: Refactor tool events

[Namhyung Kim]

Hi Ian,

On Sat, Apr 27, 2024 at 10:36 PM Ian Rogers <irogers@xxxxxxxxxx> wrote:
>
> Tool events unnecessarily open a dummy perf event which is useless
> even with `perf record` which will still open a dummy event. Change
> the behavior of tool events so:

Right, I was surprised that we need a dummy event for that.

>
>  - duration_time - call `rdclock` on open and then report the count as
>    a delta since the start in evsel__read_counter. This moves code out
>    of builtin-stat making it more general purpose.
>
>  - user_time/system_time - open the fd as either `/proc/pid/stat` or
>    `/proc/stat` for cases like system wide. evsel__read_counter will
>    read the appropriate field out of the procfs file. These values
>    were previously supplied by wait4, if the procfs read fails then
>    the wait4 values are used, assuming the process/thread terminated.
>    By reading user_time and system_time this way, interval mode can be
>    supported.

Good improvement!

>
> Opening any of the tool events for `perf record` returns invalid.

Ok, I think those tool events are for `perf stat` only.

But I feel like this change is a separate optimization and can be
independently submitted (from the retire-latency or tPEBS change).

>
> Signed-off-by: Ian Rogers <irogers@xxxxxxxxxx>
> ---
>  tools/perf/builtin-stat.c |  74 ++++++-------
>  tools/perf/util/evsel.c   | 223 +++++++++++++++++++++++++++++++++++++-
>  tools/perf/util/evsel.h   |   6 +
>  3 files changed, 259 insertions(+), 44 deletions(-)
>
> diff --git a/tools/perf/builtin-stat.c b/tools/perf/builtin-stat.c
> index 65a3dd7ffac3..428e9721b908 100644
> --- a/tools/perf/builtin-stat.c
> +++ b/tools/perf/builtin-stat.c
> @@ -255,45 +255,37 @@ static int evsel__write_stat_event(struct evsel *counter, int cpu_map_idx, u32 t
>                                            process_synthesized_event, NULL);
>  }
>
> -static int read_single_counter(struct evsel *counter, int cpu_map_idx,
> -                              int thread, struct timespec *rs)
> -{
> -       switch(counter->tool_event) {
> -               case PERF_TOOL_DURATION_TIME: {
> -                       u64 val = rs->tv_nsec + rs->tv_sec*1000000000ULL;
> -                       struct perf_counts_values *count =
> -                               perf_counts(counter->counts, cpu_map_idx, thread);
> -                       count->ena = count->run = val;
> -                       count->val = val;
> -                       return 0;
> -               }
> -               case PERF_TOOL_USER_TIME:
> -               case PERF_TOOL_SYSTEM_TIME: {
> -                       u64 val;
> -                       struct perf_counts_values *count =
> -                               perf_counts(counter->counts, cpu_map_idx, thread);
> -                       if (counter->tool_event == PERF_TOOL_USER_TIME)
> -                               val = ru_stats.ru_utime_usec_stat.mean;
> -                       else
> -                               val = ru_stats.ru_stime_usec_stat.mean;
> -                       count->ena = count->run = val;
> -                       count->val = val;
> -                       return 0;
> -               }
> -               default:
> -               case PERF_TOOL_NONE:
> -                       return evsel__read_counter(counter, cpu_map_idx, thread);
> -               case PERF_TOOL_MAX:
> -                       /* This should never be reached */
> -                       return 0;
> +static int read_single_counter(struct evsel *counter, int cpu_map_idx, int thread)
> +{
> +       int err = evsel__read_counter(counter, cpu_map_idx, thread);
> +
> +       /*
> +        * Reading user and system time will fail when the process
> +        * terminates. Use the wait4 values in that case.
> +        */
> +       if (err &&
> +           (counter->tool_event == PERF_TOOL_USER_TIME ||
> +            counter->tool_event == PERF_TOOL_SYSTEM_TIME)) {

Off-topic.  I feel like we should have a (fake) pmu for the tool events
rather than the evsel->tool_event enum.


> +               u64 val;
> +               struct perf_counts_values *count =
> +                       perf_counts(counter->counts, cpu_map_idx, thread);
> +
> +               if (counter->tool_event == PERF_TOOL_USER_TIME)
> +                       val = ru_stats.ru_utime_usec_stat.mean;
> +               else
> +                       val = ru_stats.ru_stime_usec_stat.mean;
> +               count->ena = count->run = val;
> +               count->val = val;
> +               return 0;
>         }
> +       return err;
>  }
>
>  /*
>   * Read out the results of a single counter:
>   * do not aggregate counts across CPUs in system-wide mode
>   */
> -static int read_counter_cpu(struct evsel *counter, struct timespec *rs, int cpu_map_idx)
> +static int read_counter_cpu(struct evsel *counter, int cpu_map_idx)
>  {
>         int nthreads = perf_thread_map__nr(evsel_list->core.threads);
>         int thread;
> @@ -311,7 +303,7 @@ static int read_counter_cpu(struct evsel *counter, struct timespec *rs, int cpu_
>                  * (via evsel__read_counter()) and sets their count->loaded.
>                  */
>                 if (!perf_counts__is_loaded(counter->counts, cpu_map_idx, thread) &&
> -                   read_single_counter(counter, cpu_map_idx, thread, rs)) {
> +                   read_single_counter(counter, cpu_map_idx, thread)) {
>                         counter->counts->scaled = -1;
>                         perf_counts(counter->counts, cpu_map_idx, thread)->ena = 0;
>                         perf_counts(counter->counts, cpu_map_idx, thread)->run = 0;
> @@ -340,7 +332,7 @@ static int read_counter_cpu(struct evsel *counter, struct timespec *rs, int cpu_
>         return 0;
>  }
>
> -static int read_affinity_counters(struct timespec *rs)
> +static int read_affinity_counters(void)
>  {
>         struct evlist_cpu_iterator evlist_cpu_itr;
>         struct affinity saved_affinity, *affinity;
> @@ -361,10 +353,8 @@ static int read_affinity_counters(struct timespec *rs)
>                 if (evsel__is_bpf(counter))
>                         continue;
>
> -               if (!counter->err) {
> -                       counter->err = read_counter_cpu(counter, rs,
> -                                                       evlist_cpu_itr.cpu_map_idx);
> -               }
> +               if (!counter->err)
> +                       counter->err = read_counter_cpu(counter, evlist_cpu_itr.cpu_map_idx);
>         }
>         if (affinity)
>                 affinity__cleanup(&saved_affinity);
> @@ -388,11 +378,11 @@ static int read_bpf_map_counters(void)
>         return 0;
>  }
>
> -static int read_counters(struct timespec *rs)
> +static int read_counters(void)
>  {
>         if (!stat_config.stop_read_counter) {
>                 if (read_bpf_map_counters() ||
> -                   read_affinity_counters(rs))
> +                   read_affinity_counters())
>                         return -1;
>         }
>         return 0;
> @@ -423,7 +413,7 @@ static void process_interval(void)
>
>         evlist__reset_aggr_stats(evsel_list);
>
> -       if (read_counters(&rs) == 0)
> +       if (read_counters() == 0)
>                 process_counters();
>
>         if (STAT_RECORD) {
> @@ -911,7 +901,7 @@ static int __run_perf_stat(int argc, const char **argv, int run_idx)
>          * avoid arbitrary skew, we must read all counters before closing any
>          * group leaders.
>          */
> -       if (read_counters(&(struct timespec) { .tv_nsec = t1-t0 }) == 0)
> +       if (read_counters() == 0)
>                 process_counters();
>
>         /*

I think this part can be a separate commit.  You can implement the
tool event handling before actually using it. :)


> diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c
> index 3536404e9447..a0a8aee7d6b9 100644
> --- a/tools/perf/util/evsel.c
> +++ b/tools/perf/util/evsel.c
> @@ -10,6 +10,7 @@
>  #include <errno.h>
>  #include <inttypes.h>
>  #include <linux/bitops.h>
> +#include <api/io.h>
>  #include <api/fs/fs.h>
>  #include <api/fs/tracing_path.h>
>  #include <linux/hw_breakpoint.h>
> @@ -30,6 +31,7 @@
>  #include "counts.h"
>  #include "event.h"
>  #include "evsel.h"
> +#include "time-utils.h"
>  #include "util/env.h"
>  #include "util/evsel_config.h"
>  #include "util/evsel_fprintf.h"
> @@ -1600,11 +1602,183 @@ static int evsel__read_group(struct evsel *leader, int cpu_map_idx, int thread)
>         return evsel__process_group_data(leader, cpu_map_idx, thread, data);
>  }
>
> +static int read_stat_field(int fd, struct perf_cpu cpu, int field, __u64 *val)
> +{
> +       char buf[256];
> +       struct io io;
> +       int c, i;
> +
> +       io__init(&io, fd, buf, sizeof(buf));
> +
> +       /* Skip lines to relevant CPU. */
> +       for (i = -1; i < cpu.cpu; i++) {
> +               do {
> +                       c = io__get_char(&io);
> +                       if (c == -1)
> +                               return -EINVAL;
> +               } while (c != '\n');
> +       }
> +       /* Skip to "cpu". */
> +       c = io__get_char(&io);
> +       if (c != 'c')
> +               return -EINVAL;
> +       c = io__get_char(&io);
> +       if (c != 'p')
> +               return -EINVAL;
> +       c = io__get_char(&io);
> +       if (c != 'u')
> +               return -EINVAL;
> +       /* Skip N of cpuN. */
> +       do {
> +               c = io__get_char(&io);
> +               if (c == -1)
> +                       return -EINVAL;
> +       } while (c != ' ');
> +
> +       i = 1;
> +       while (true) {
> +               c = io__get_dec(&io, val);
> +               if (c != ' ')
> +                       break;
> +               if (field == i)
> +                       return 0;
> +               i++;
> +       }
> +       return -EINVAL;
> +}

Looks somewhat verbose, can we have something like
io__get_str_field() or io__get_num_filed()?


> +
> +static int read_pid_stat_field(int fd, int field, __u64 *val)
> +{
> +       char buf[256];
> +       struct io io;
> +       int c, i;
> +
> +       io__init(&io, fd, buf, sizeof(buf));
> +       c = io__get_dec(&io, val);
> +       if (c != ' ')
> +               return -EINVAL;
> +       if (field == 1)
> +               return 0;
> +
> +       /* Skip comm. */
> +       c = io__get_char(&io);
> +       if (c != '(')
> +               return -EINVAL;
> +       do {
> +               c = io__get_char(&io);
> +               if (c == -1)
> +                       return -EINVAL;
> +       } while (c != ')');
> +       if (field == 2)
> +               return -EINVAL;
> +
> +       /* Skip state */
> +       c = io__get_char(&io);
> +       if (c != ' ')
> +               return -EINVAL;
> +       c = io__get_char(&io);
> +       if (c == -1)
> +               return -EINVAL;
> +       if (field == 3)
> +               return -EINVAL;
> +
> +       /* Loop over numeric fields*/
> +       c = io__get_char(&io);
> +       if (c != ' ')
> +               return -EINVAL;
> +
> +       i = 4;
> +       while (true) {
> +               c = io__get_dec(&io, val);
> +               if (c == -1)
> +                       return -EINVAL;
> +               if (c == -2) {
> +                       /* Assume a -ve was read */
> +                       c = io__get_dec(&io, val);
> +                       *val *= -1;
> +               }
> +               if (c != ' ')
> +                       return -EINVAL;
> +               if (field == i)
> +                       return 0;
> +               i++;
> +       }
> +       return -EINVAL;
> +}
> +
> +static int evsel__read_tool(struct evsel *evsel, int cpu_map_idx, int thread)
> +{
> +       __u64 cur_time, delta_start;
> +       int fd, err = 0;
> +       struct perf_counts_values *count;
> +       bool adjust = false;
> +
> +       count = perf_counts(evsel->counts, cpu_map_idx, thread);
> +
> +       switch (evsel->tool_event) {
> +       case PERF_TOOL_DURATION_TIME:
> +               /*
> +                * Pretend duration_time is only on the first CPU and thread, or
> +                * else aggregation will scale duration_time by the number of
> +                * CPUs/threads.
> +                */

We could set evsel->pmu->cpus to 0, if there's a tool pmu.


> +               if (cpu_map_idx == 0 && thread == 0)
> +                       cur_time = rdclock();
> +               else
> +                       cur_time = evsel->start_time;
> +               break;
> +       case PERF_TOOL_USER_TIME:
> +       case PERF_TOOL_SYSTEM_TIME: {
> +               bool system = evsel->tool_event == PERF_TOOL_SYSTEM_TIME;
> +
> +               fd = FD(evsel, cpu_map_idx, thread);
> +               lseek(fd, SEEK_SET, 0);
> +               if (evsel->pid_stat) {
> +                       /* The event exists solely on 1 CPU. */

Probably the same.

Thanks,
Namhyung


> +                       if (cpu_map_idx == 0)
> +                               err = read_pid_stat_field(fd, system ? 15 : 14, &cur_time);
> +                       else
> +                               cur_time = 0;
> +               } else {
> +                       /* The event is for all threads. */
> +                       if (thread == 0) {
> +                               struct perf_cpu cpu = perf_cpu_map__cpu(evsel->core.cpus,
> +                                                                       cpu_map_idx);
> +
> +                               err = read_stat_field(fd, cpu, system ? 3 : 1, &cur_time);
> +                       } else {
> +                               cur_time = 0;
> +                       }
> +               }
> +               adjust = true;
> +               break;
> +       }
> +       case PERF_TOOL_NONE:
> +       case PERF_TOOL_MAX:
> +       default:
> +               err = -EINVAL;
> +       }
> +       if (err)
> +               return err;
> +
> +       delta_start = cur_time - evsel->start_time;
> +       if (adjust) {
> +               __u64 ticks_per_sec = sysconf(_SC_CLK_TCK);
> +
> +               delta_start *= 1000000000 / ticks_per_sec;
> +       }
> +       count->val    = delta_start;
> +       count->ena    = count->run = delta_start;
> +       count->lost   = 0;
> +       return 0;
> +}
> +
>  int evsel__read_counter(struct evsel *evsel, int cpu_map_idx, int thread)
>  {
> -       u64 read_format = evsel->core.attr.read_format;
> +       if (evsel__is_tool(evsel))
> +               return evsel__read_tool(evsel, cpu_map_idx, thread);
>
> -       if (read_format & PERF_FORMAT_GROUP)
> +       if (evsel->core.attr.read_format & PERF_FORMAT_GROUP)
>                 return evsel__read_group(evsel, cpu_map_idx, thread);
>
>         return evsel__read_one(evsel, cpu_map_idx, thread);
> @@ -2005,6 +2179,13 @@ static int evsel__open_cpu(struct evsel *evsel, struct perf_cpu_map *cpus,
>         int pid = -1, err, old_errno;
>         enum rlimit_action set_rlimit = NO_CHANGE;
>
> +       if (evsel->tool_event == PERF_TOOL_DURATION_TIME) {
> +               if (evsel->core.attr.sample_period) /* no sampling */
> +                       return -EINVAL;
> +               evsel->start_time = rdclock();
> +               return 0;
> +       }
> +
>         err = __evsel__prepare_open(evsel, cpus, threads);
>         if (err)
>                 return err;
> @@ -2037,6 +2218,44 @@ static int evsel__open_cpu(struct evsel *evsel, struct perf_cpu_map *cpus,
>                         if (!evsel->cgrp && !evsel->core.system_wide)
>                                 pid = perf_thread_map__pid(threads, thread);
>
> +                       if (evsel->tool_event == PERF_TOOL_USER_TIME ||
> +                           evsel->tool_event == PERF_TOOL_SYSTEM_TIME) {
> +                               bool system = evsel->tool_event == PERF_TOOL_SYSTEM_TIME;
> +
> +                               if (evsel->core.attr.sample_period) {
> +                                       /* no sampling */
> +                                       err = -EINVAL;
> +                                       goto out_close;
> +                               }
> +                               if (pid > -1) {
> +                                       char buf[64];
> +
> +                                       snprintf(buf, sizeof(buf), "/proc/%d/stat", pid);
> +                                       fd = open(buf, O_RDONLY);
> +                                       evsel->pid_stat = true;
> +                               } else {
> +                                       fd = open("/proc/stat", O_RDONLY);
> +                               }
> +                               FD(evsel, idx, thread) = fd;
> +                               if (fd < 0) {
> +                                       err = -errno;
> +                                       goto out_close;
> +                               }
> +                               if (pid > -1) {
> +                                       err = read_pid_stat_field(fd, system ? 15 : 14,
> +                                                                 &evsel->start_time);
> +                               } else {
> +                                       struct perf_cpu cpu;
> +
> +                                       cpu = perf_cpu_map__cpu(evsel->core.cpus, idx);
> +                                       err = read_stat_field(fd, cpu, system ? 3 : 1,
> +                                                             &evsel->start_time);
> +                               }
> +                               if (err)
> +                                       goto out_close;
> +                               continue;
> +                       }
> +
>                         group_fd = get_group_fd(evsel, idx, thread);
>
>                         if (group_fd == -2) {
> diff --git a/tools/perf/util/evsel.h b/tools/perf/util/evsel.h
> index 517cff431de2..43f6fd1dcb4d 100644
> --- a/tools/perf/util/evsel.h
> +++ b/tools/perf/util/evsel.h
> @@ -170,6 +170,12 @@ struct evsel {
>
>         /* for missing_features */
>         struct perf_pmu         *pmu;
> +
> +       /* For tool events */
> +       /* Beginning time subtracted when the counter is read. */
> +       __u64 start_time;
> +       /* Is the tool's fd for /proc/pid/stat or /proc/stat. */
> +       bool pid_stat;
>  };
>
>  struct perf_missing_features {
> --
> 2.44.0.769.g3c40516874-goog
>