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Message-ID: <90d877df-523e-6277-717e-9d63f2efccc5@intel.com>
Date: Fri, 25 Aug 2023 09:13:28 +0300
From: Adrian Hunter <adrian.hunter@...el.com>
To: Ian Rogers <irogers@...gle.com>,
Yang Jihong <yangjihong1@...wei.com>
Cc: peterz@...radead.org, mingo@...hat.com, acme@...nel.org,
mark.rutland@....com, alexander.shishkin@...ux.intel.com,
jolsa@...nel.org, namhyung@...nel.org, kan.liang@...ux.intel.com,
james.clark@....com, tmricht@...ux.ibm.com, ak@...ux.intel.com,
anshuman.khandual@....com, linux-kernel@...r.kernel.org,
linux-perf-users@...r.kernel.org
Subject: Re: [PATCH v6 4/7] perf record: Track sideband events for all CPUs
when tracing selected CPUs
On 25/08/23 08:17, Ian Rogers wrote:
> On Sun, Aug 20, 2023 at 6:30 PM Yang Jihong <yangjihong1@...wei.com> 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_MMAP events of taskA.
>> Therefore, the comm and symbols of taskA cannot be parsed.
>>
>> The solution is to record sideband events for all CPUs when tracing
>> selected CPUs. Because this modifies the default behavior, add related
>> comments to the perf record man page.
>>
>> 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 (PERF_TYPE_SOFTWARE)
>> size 136
>> config 0 (PERF_COUNT_SW_CPU_CLOCK)
>> { sample_period, sample_freq } 4000
>> sample_type IP|TID|TIME|CPU|PERIOD|IDENTIFIER
>> 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:u
>> ------------------------------------------------------------
>> perf_event_attr:
>> type 1 (PERF_TYPE_SOFTWARE)
>> size 136
>> config 0x9 (PERF_COUNT_SW_DUMMY)
>> { sample_period, sample_freq } 1
>> sample_type IP|TID|TIME|CPU|IDENTIFIER
>> read_format ID|LOST
>> inherit 1
>> exclude_kernel 1
>> exclude_hv 1
>> mmap 1
>> comm 1
>> task 1
>> sample_id_all 1
>> exclude_guest 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>
>> Acked-by: Adrian Hunter <adrian.hunter@...el.com>
>> ---
>> tools/perf/Documentation/perf-record.txt | 3 ++
>> tools/perf/builtin-record.c | 44 +++++++++++++++++++++++-
>> 2 files changed, 46 insertions(+), 1 deletion(-)
>>
>> diff --git a/tools/perf/Documentation/perf-record.txt b/tools/perf/Documentation/perf-record.txt
>> index d5217be012d7..1889f66addf2 100644
>> --- a/tools/perf/Documentation/perf-record.txt
>> +++ b/tools/perf/Documentation/perf-record.txt
>> @@ -374,6 +374,9 @@ comma-separated list with no space: 0,1. Ranges of CPUs are specified with -: 0-
>> In per-thread mode with inheritance mode on (default), samples are captured only when
>> the thread executes on the designated CPUs. Default is to monitor all CPUs.
>>
>> +User space tasks can migrate between CPUs, so when tracing selected CPUs,
>> +a dummy event is created to track sideband for all CPUs.
>> +
>> -B::
>> --no-buildid::
>> Do not save the build ids of binaries in the perf.data files. This skips
>> diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
>> index 4ee94058028f..ae2e21b945fa 100644
>> --- a/tools/perf/builtin-record.c
>> +++ b/tools/perf/builtin-record.c
>> @@ -906,10 +906,44 @@ static int record__config_off_cpu(struct record *rec)
>> return off_cpu_prepare(rec->evlist, &rec->opts.target, &rec->opts);
>> }
>>
>> +static bool record__tracking_system_wide(struct record *rec)
>
> I think this would be better named something like:
> record__need_system_wide_dummy_event
Please no. The tracking event is a perf tool invention identified
by evsel->tracking and used in evsel__config(). Please don't
confuse it with dummy events. Just because the tracking event
*might* be a dummy event does not mean a dummy event is the
tracking event.
>
> Thanks,
> Ian
>
>> +{
>> + struct record_opts *opts = &rec->opts;
>> + struct evlist *evlist = rec->evlist;
>> + struct evsel *evsel;
>> +
>> + /*
>> + * If all (non-dummy) evsel have exclude_user,
>> + * system_wide is not needed.
>> + *
>> + * all_kernel and all_user will overwrite exclude_kernel and
>> + * exclude_user of attr in evsel__config(), here need to check
>> + * all the three items.
>> + *
>> + * Sideband system wide if one of the following conditions is met:
>> + *
>> + * - all_user is set, and there is a non-dummy event
>> + * - all_user and all_kernel are not set, and there is
>> + * a non-dummy event without exclude_user
>> + */
>> + if (opts->all_kernel)
>> + return false;
>> +
>> + evlist__for_each_entry(evlist, evsel) {
>> + if (!evsel__is_dummy_event(evsel)) {
>> + if (opts->all_user || !evsel->core.attr.exclude_user)
>> + return true;
>> + }
>> + }
>> +
>> + return false;
>> +}
>> +
>> static int record__config_tracking_events(struct record *rec)
>> {
>> struct record_opts *opts = &rec->opts;
>> struct evlist *evlist = rec->evlist;
>> + bool system_wide = false;
>> struct evsel *evsel;
>>
>> /*
>> @@ -919,7 +953,15 @@ static int record__config_tracking_events(struct record *rec)
>> */
>> if (opts->target.initial_delay || target__has_cpu(&opts->target) ||
>> perf_pmus__num_core_pmus() > 1) {
>> - evsel = evlist__findnew_tracking_event(evlist, false);
>> +
>> + /*
>> + * User space tasks can migrate between CPUs, so when tracing
>> + * selected CPUs, sideband for all CPUs is still needed.
>> + */
>> + if (!!opts->target.cpu_list && record__tracking_system_wide(rec))
>> + system_wide = true;
>> +
>> + evsel = evlist__findnew_tracking_event(evlist, system_wide);
>> if (!evsel)
>> return -ENOMEM;
>>
>> --
>> 2.30.GIT
>>
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