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Date: Tue, 11 Jul 2023 16:13:26 +0300
From: Adrian Hunter <adrian.hunter@...el.com>
To: Yang Jihong <yangjihong1@...wei.com>, peterz@...radead.org,
mingo@...hat.com, acme@...nel.org, mark.rutland@....com,
alexander.shishkin@...ux.intel.com, jolsa@...nel.org,
namhyung@...nel.org, irogers@...gle.com, kan.liang@...ux.intel.com,
linux-kernel@...r.kernel.org, linux-perf-users@...r.kernel.org
Subject: Re: [PATCH 3/5] perf record: Tracking side-band events for all CPUs
when tracing selected CPUs
On 4/07/23 10:42, Yang Jihong wrote:
> User space tasks can migrate between CPUs, we need to track side-band
> events for all CPUs.
>
> The specific scenarios are as follows:
>
> CPU0 CPU1
> perf record -C 0 start
> taskA starts to be created and executed
> -> PERF_RECORD_COMM and PERF_RECORD_MMAP
> events only deliver to CPU1
> ......
> |
> migrate to CPU0
> |
> Running on CPU0 <----------/
> ...
>
> perf record -C 0 stop
>
> Now perf samples the PC of taskA. However, perf does not record the
> PERF_RECORD_COMM and PERF_RECORD_COMM events of taskA.
> Therefore, the comm and symbols of taskA cannot be parsed.
>
> The sys_perf_event_open invoked is as follows:
>
> # perf --debug verbose=3 record -e cpu-clock -C 1 true
> <SNIP>
> Opening: cpu-clock
> ------------------------------------------------------------
> perf_event_attr:
> type 1
> size 136
> { sample_period, sample_freq } 4000
> sample_type IP|TID|TIME|ID|CPU|PERIOD
> read_format ID|LOST
> disabled 1
> inherit 1
> freq 1
> sample_id_all 1
> exclude_guest 1
> ------------------------------------------------------------
> sys_perf_event_open: pid -1 cpu 1 group_fd -1 flags 0x8 = 5
> Opening: dummy:HG
> ------------------------------------------------------------
> perf_event_attr:
> type 1
> size 136
> config 0x9
> { sample_period, sample_freq } 4000
> sample_type IP|TID|TIME|ID|CPU|PERIOD
> read_format ID|LOST
> inherit 1
> mmap 1
> comm 1
> freq 1
> task 1
> sample_id_all 1
> mmap2 1
> comm_exec 1
> ksymbol 1
> bpf_event 1
> ------------------------------------------------------------
> sys_perf_event_open: pid -1 cpu 0 group_fd -1 flags 0x8 = 6
> sys_perf_event_open: pid -1 cpu 1 group_fd -1 flags 0x8 = 7
> sys_perf_event_open: pid -1 cpu 2 group_fd -1 flags 0x8 = 9
> sys_perf_event_open: pid -1 cpu 3 group_fd -1 flags 0x8 = 10
> sys_perf_event_open: pid -1 cpu 4 group_fd -1 flags 0x8 = 11
> sys_perf_event_open: pid -1 cpu 5 group_fd -1 flags 0x8 = 12
> sys_perf_event_open: pid -1 cpu 6 group_fd -1 flags 0x8 = 13
> sys_perf_event_open: pid -1 cpu 7 group_fd -1 flags 0x8 = 14
> <SNIP>
>
> Signed-off-by: Yang Jihong <yangjihong1@...wei.com>
> ---
> tools/perf/builtin-record.c | 31 +++++++++++++++++++++++++++++++
> 1 file changed, 31 insertions(+)
>
> diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
> index 8872cd037f2c..69e0d8c75aab 100644
> --- a/tools/perf/builtin-record.c
> +++ b/tools/perf/builtin-record.c
> @@ -908,6 +908,31 @@ static int record__config_off_cpu(struct record *rec)
> return off_cpu_prepare(rec->evlist, &rec->opts.target, &rec->opts);
> }
>
> +static int record__config_tracking_events(struct record *rec)
> +{
> + struct evsel *evsel;
> + struct evlist *evlist = rec->evlist;
> + struct record_opts *opts = &rec->opts;
> +
> + /*
> + * User space tasks can migrate between CPUs, so when tracing
> + * selected CPUs, sideband for all CPUs is still needed.
> + */
> + if (opts->target.cpu_list) {
I am not sure if anyone minds doing this by default, but perhaps
we should say something about it on the perf record man page.
> + evsel = evlist__findnew_tracking_event(evlist);
> + if (!evsel)
> + return -ENOMEM;
> +
> + if (!evsel->core.system_wide) {
> + evsel->core.system_wide = true;
> + evsel__set_sample_bit(evsel, TIME);
> + perf_evlist__propagate_maps(&evlist->core, &evsel->core);
> + }
Perhaps better to export via internel/evsel.h
void perf_evsel__go_system_wide(struct perf_evlist *evlist, struct perf_evsel *evsel)
{
if (!evsel->system_wide) {
evsel->system_wide = true;
if (evlist->needs_map_propagation)
__perf_evlist__propagate_maps(evlist, evsel);
}
}
As suggested in response to patch 2, perhaps deal with system_wide
inside evlist__findnew_tracking_event()
> + }
> +
> + return 0;
> +}
> +
> static bool record__kcore_readable(struct machine *machine)
> {
> char kcore[PATH_MAX];
> @@ -4235,6 +4260,12 @@ int cmd_record(int argc, const char **argv)
> goto out;
> }
>
> + err = record__config_tracking_events(rec);
> + if (err) {
> + pr_err("record__config_tracking_events failed, error %d\n", err);
> + goto out;
> + }
> +
> err = record__init_thread_masks(rec);
> if (err) {
> pr_err("Failed to initialize parallel data streaming masks\n");
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