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Date:   Fri, 17 Jul 2020 14:40:53 -0300
From:   Arnaldo Carvalho de Melo <acme@...nel.org>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Changbin Du <changbin.du@...il.com>,
        Arnaldo Carvalho de Melo <arnaldo.melo@...il.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 03/17] perf ftrace: add option -t/--tid to filter by
 thread id

Em Fri, Jul 17, 2020 at 01:01:24PM -0400, Steven Rostedt escreveu:
> On Fri, 17 Jul 2020 21:26:50 +0800
> Changbin Du <changbin.du@...il.com> wrote:
> 
> > On Thu, Jul 16, 2020 at 12:36:30PM -0300, Arnaldo Carvalho de Melo wrote:
> > > Em Sat, Jul 11, 2020 at 08:40:21PM +0800, Changbin Du escreveu:  
> > > > This allows us to trace single thread instead of the whole process.
> > > > 
> > > > Signed-off-by: Changbin Du <changbin.du@...il.com>
> > > > ---
> > > >  tools/perf/Documentation/perf-ftrace.txt | 4 ++++
> > > >  tools/perf/builtin-ftrace.c              | 2 ++
> > > >  2 files changed, 6 insertions(+)
> > > > 
> > > > diff --git a/tools/perf/Documentation/perf-ftrace.txt b/tools/perf/Documentation/perf-ftrace.txt
> > > > index d79560dea19f..e204bf6d50d8 100644
> > > > --- a/tools/perf/Documentation/perf-ftrace.txt
> > > > +++ b/tools/perf/Documentation/perf-ftrace.txt
> > > > @@ -38,6 +38,10 @@ OPTIONS
> > > >  --pid=::
> > > >  	Trace on existing process id (comma separated list).
> > > >  
> > > > +-t::
> > > > +--tid=::
> > > > +	Trace on existing thread id (comma separated list).
> > > > +  

> > > Humm, I just  tried:

> > > [root@...e ~]# yes > /dev/null &
> > > [1] 18265
> > > [root@...e ~]# perf ftrace --tid 18265
> > > ^C[root@...e ~]#

> > > After waiting for a while, nothing, what am I doing wrong?

> > I got it wrong. Currently ftrace only can filter by pid. If the pid is not
> > the main thread it won't work.
 
> Wait what?
 
> The "pid" for ftrace is really a "task id" which is a thread id.
 
> [root@...est ~]# yes > /dev/null &
> [1] 6799
> [root@...est ~]# trace-cmd record -e all -P 6799
> Hit Ctrl^C to stop recording
> ^CCPU 0: 3573031 events lost
> CPU0 data recorded at offset=0x838000
>     627675136 bytes in size
> CPU1 data recorded at offset=0x25ed1000
>     0 bytes in size
> CPU2 data recorded at offset=0x25ed1000
>     0 bytes in size
> CPU3 data recorded at offset=0x25ed1000
>     0 bytes in size
> CPU4 data recorded at offset=0x25ed1000
>     0 bytes in size
> CPU5 data recorded at offset=0x25ed1000
>     0 bytes in size
> CPU6 data recorded at offset=0x25ed1000
>     0 bytes in size
> CPU7 data recorded at offset=0x25ed1000
>     0 bytes in size
> [root@...est ~]# trace-cmd report | head 
> CPU 1 is empty
> CPU 2 is empty
> CPU 3 is empty
> CPU 4 is empty
> CPU 5 is empty
> CPU 6 is empty
> CPU 7 is empty
> cpus=8
>              yes-6799  [000] 67825.580902: sys_exit:             NR 1 = 8192
>              yes-6799  [000] 67825.580903: sys_exit_write:       0x2000
> 
> 
> What's different about tid vs pid?

Say you use:

^C[root@...andy ~]# cyclictest --smp -um -p95
# /dev/cpu_dma_latency set to 0us
policy: fifo: loadavg: 0.05 0.03 0.06 2/409 29072

T: 0 (29065) P:95 I:1000 C:    518 Min:      2 Act:    2 Avg:    2 Max:       6
T: 1 (29066) P:95 I:1500 C:    343 Min:      2 Act:    2 Avg:    2 Max:       5
T: 2 (29067) P:95 I:2000 C:    256 Min:      2 Act:    2 Avg:    2 Max:       7
T: 3 (29068) P:95 I:2500 C:    203 Min:      2 Act:    2 Avg:    2 Max:       5
T: 4 (29069) P:95 I:3000 C:    168 Min:      2 Act:    2 Avg:    3 Max:       6
T: 5 (29070) P:95 I:3500 C:    143 Min:      2 Act:    2 Avg:    2 Max:       6
T: 6 (29071) P:95 I:4000 C:    124 Min:      2 Act:    2 Avg:    2 Max:       7
T: 7 (29072) P:95 I:4500 C:    110 Min:      2 Act:    2 Avg:    2 Max:

Then we do:

# pidof cyclictest
29064
#

If we use:

[root@...andy ~]# perf record --pid 29064
^C[ perf record: Woken up 1 times to write data ]
[ perf record: Captured and wrote 0.052 MB perf.data (866 samples) ]

[root@...andy ~]# perf report --task
#      pid      tid     ppid  comm
         0        0       -1 |swapper
     29064    29064       -1 |cyclictest
     29064    29065       -1 |cyclictest
     29064    29066       -1 |cyclictest
     29064    29067       -1 |cyclictest
     29064    29068       -1 |cyclictest
     29064    29069       -1 |cyclictest
     29064    29070       -1 |cyclictest
     29064    29071       -1 |cyclictest
     29064    29072       -1 |cyclictest
[root@...andy ~]#

If we are interested only on the thread running on CPU3 we can do:

[root@...andy ~]# perf report --task
#      pid      tid     ppid  comm
         0        0       -1 |swapper
     29064    29064       -1 |cyclictest
     29064    29068       -1 |cyclictest
[root@...andy ~]#

The first 29064 is just to have info on who created 29068, i.e.:

Its just the synthesized info for 29068 creator:

[root@...andy ~]# perf report -D | grep -w 29064/29064
0 0x4690 [0x30]: PERF_RECORD_COMM: cyclictest:29064/29064
0 0x46c0 [0x70]: PERF_RECORD_MMAP2 29064/29064: [0x400000(0xa000) @ 0 fd:00 136246288 0]: r-xp /usr/bin/cyclictest
0 0x4730 [0x80]: PERF_RECORD_MMAP2 29064/29064: [0x7f990f505000(0x15000) @ 0 fd:00 201479398 0]: r-xp /usr/lib64/libgcc_s-4.8.5-20150702.so.1
0 0x47b0 [0x70]: PERF_RECORD_MMAP2 29064/29064: [0x7f990f71b000(0x1c3000) @ 0 fd:00 201334455 0]: r-xp /usr/lib64/libc-2.17.so
0 0x4820 [0x78]: PERF_RECORD_MMAP2 29064/29064: [0x7f990fae9000(0xa000) @ 0 fd:00 204604380 0]: r-xp /usr/lib64/libnuma.so.1.0.0
0 0x4898 [0x78]: PERF_RECORD_MMAP2 29064/29064: [0x7f990fcf5000(0x17000) @ 0 fd:00 201335636 0]: r-xp /usr/lib64/libpthread-2.17.so
0 0x4910 [0x78]: PERF_RECORD_MMAP2 29064/29064: [0x7f990ff11000(0x7000) @ 0 fd:00 201335640 0]: r-xp /usr/lib64/librt-2.17.so
0 0x4988 [0x70]: PERF_RECORD_MMAP2 29064/29064: [0x7f9910119000(0x22000) @ 0 fd:00 203595299 0]: r-xp /usr/lib64/ld-2.17.so
0 0x49f8 [0x60]: PERF_RECORD_MMAP2 29064/29064: [0x7fff0b52d000(0x2000) @ 0 00:00 0 0]: r-xp [vdso]
0 0x4a58 [0x68]: PERF_RECORD_MMAP2 29064/29064: [0xffffffffff600000(0x1000) @ 0 00:00 0 0]: r-xp [vsyscall]
[root@...andy ~]#

No PERF_RECORD_SAMPLEs.

Those are only for:

[root@...andy ~]# perf report -D | grep PERF_RECORD_SAMPLE | head -5
147224656598815 0x4ac0 [0x28]: PERF_RECORD_SAMPLE(IP, 0x4001): 29064/29068: 0xffffffffa8e5b568 period: 1 addr: 0
147224656606270 0x4ae8 [0x28]: PERF_RECORD_SAMPLE(IP, 0x4001): 29064/29068: 0xffffffffa8e5b568 period: 1 addr: 0
147224656611284 0x4b10 [0x28]: PERF_RECORD_SAMPLE(IP, 0x4001): 29064/29068: 0xffffffffa8e5b568 period: 5 addr: 0
147224656616225 0x4b38 [0x28]: PERF_RECORD_SAMPLE(IP, 0x4001): 29064/29068: 0xffffffffa8e5b568 period: 35 addr: 0
147224656621152 0x4b60 [0x28]: PERF_RECORD_SAMPLE(IP, 0x4001): 29064/29068: 0xffffffffa8e5b568 period: 252 addr: 0
[root@...andy ~]#

[root@...andy ~]# perf report -D | grep PERF_RECORD_SAMPLE | cut -d: -f3 | sort -u
 29064/29068
[root@...andy ~]#

Is there a way in ftrace to ask for a pid and its children? Pre-existing
and and new ones the --pid specified will create after we start
monitoring?

- Arnaldo

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