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Date: Tue, 29 Aug 2023 09:40:42 +0800
From: Yang Jihong <yangjihong1@...wei.com>
To: Adrian Hunter <adrian.hunter@...el.com>,
Namhyung Kim <namhyung@...nel.org>
CC: <peterz@...radead.org>, <mingo@...hat.com>, <acme@...nel.org>,
<mark.rutland@....com>, <alexander.shishkin@...ux.intel.com>,
<jolsa@...nel.org>, <irogers@...gle.com>,
<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 v7 4/6] perf record: Track sideband events for all CPUs
when tracing selected CPUs
Hello,
On 2023/8/28 19:25, Adrian Hunter wrote:
> On 28/08/23 06:03, Yang Jihong wrote:
>> Hello,
>>
>> On 2023/8/26 22:59, Namhyung Kim wrote:
>>> Hello,
>>>
>>> On Fri, Aug 25, 2023 at 8:29 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 83bd1f117191..21c571018148 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)
>>>> +{
>>>> + 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.
>>>
>>> Maybe I missed some earlier discussion but why is it not
>>> needed when exclude_user is set? I think it still needs
>>> FORK or COMM at least..
>>>
>>
>> This is Adrian's suggestion earlier, I think it's probably because if exclude_user is set, MMAP information is not needed, that's my guess.
>>
>> However, as you said, even if exclude_user is set, at least FORK and COMM are required.
>>
>> Therefore, the conditions here need to be changed to:
>> "system_wide is need as long as there is a non-dummy event."
>>
>> @Adrian, is this change okay?
>
> If you wish. I think we use FORK to get mappings, so not sure it
> would be needed. There is PID, TID so COMM is not essential.
> There are FORK, COMM etc from the CPUs being traced of course.
>
I think COMM is also necessary. If there is no COMM, the perf report
cannot display the comm of the process migrated from other core.
The test result is as follows:
# perf report --stdio
# To display the perf.data header info, please use
--header/--header-only options.
#
#
# Total Lost Samples: 0
#
# Samples: 33 of event 'cpu-clock:khppp'
# Event count (approx.): 8250000
#
# Overhead Command Shared Object Symbol
# ........ ............... .................
.......................................
#
15.15% test3 [kernel.kallsyms] [k] finish_task_switch
9.09% kworker/1:0-eve [kernel.kallsyms] [k] _raw_spin_unlock_irq
3.03% :934 [kernel.kallsyms] [k] blk_done_softirq
3.03% :934 [kernel.kallsyms] [k] finish_task_switch
<SNIP>
Thanks,
Yang
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