From: "Liang, Kan" <kan.liang@intel.com>
To: David Ahern <dsahern@gmail.com>, Andi Kleen <andi@firstfloor.org>
CC: Arnaldo Carvalho de Melo <acme@kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "Huang, Ying" <ying.huang@intel.com>
Subject: RE: [PATCH 1/1] perf,tools: add time out to force stop endless mmap
 processing
Thread-Topic: [PATCH 1/1] perf,tools: add time out to force stop endless
 mmap processing
Thread-Index: AQHQo44i3glIe3h0sEG/9i/L0QJfWp2m0lUAgAAU7wCAADmvgIAAYMUAgAFtkPD//5AIgIAAk2vg//+KeQCAAJJsMP//j0eAABDMbwA=
Date: Fri, 12 Jun 2015 20:39:55 +0000
Message-ID: <37D7C6CF3E00A74B8858931C1DB2F07701876D60@SHSMSX103.ccr.corp.intel.com>
References: <1433922364-22580-1-git-send-email-kan.liang@intel.com>
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 <557AFDB1.7030902@gmail.com>
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 <37D7C6CF3E00A74B8858931C1DB2F07701876CB2@SHSMSX103.ccr.corp.intel.com>
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> 
> On 6/12/15 12:19 PM, Liang, Kan wrote:
> >>> [perf]$ sudo ./perf record -e instructions:pp --pid 14560 Reading
> >>> /proc/14560/maps cost 13.12690599 s ^C[ perf record: Woken up 1
> >>> times to write data ] [ perf record: Captured and wrote 0.108 MB
> >>> perf.data
> >>> (2783 samples) ]
> >>
> >> so perf was able to read the proc file?
> >
> > Yes, perf always can read proc file. The problem is that the proc file
> > is huge and keep growing faster than proc reader.
> > So perf top do loop in perf_event__synthesize_mmap_events until the
> > test case exit.
> 
> I'm confused. How are you getting the above time to read /proc maps if it
> never finishes?

I just tried to simplify the issue for perf record. So you may noticed that
I only read one thread. There are several threads in the system.
Also, I do the perf record test when starting the test case.
The proc file is not that big.
For perf top, it will monitor whole system. So it never finishes. 

> 
> for this test case how does perf-record compare between proc and
> task_diag? You can use my command for both. It defaults to using
> task_diag and then you can add --no-task_diag to have it read /proc. And
> as mentioned before it is only setup for 'perf record -a' case. So
> 
> launch your test program
> perf record -a -- usleep 1
> perf record -a --no-task_diag -- usleep 1
> 

Here are the test results. 
Please note that I get "synthesized threads took..." after the test case exit. 
It means both way have the same issue.

[perf]$ sudo ./perf record -a -- usleep 1
  synthesized threads took 278.780762 sec
[ perf record: Woken up 1 times to write data ]
[ perf record: Captured and wrote 0.617 MB perf.data (7974 samples) ]

[perf]$ sudo ./perf record -a --no-task_diag -- usleep 1
synthesized threads took 315.612403 sec
[ perf record: Woken up 1 times to write data ]
[ perf record: Captured and wrote 0.443 MB perf.data (2754 samples) ]

Thanks,
Kan

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