linux-kernel - RE: [PATCH 1/1] perf,tools: add time out to force stop endless mmap processing

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Message-ID: <37D7C6CF3E00A74B8858931C1DB2F07701876CB2@SHSMSX103.ccr.corp.intel.com>
Date:	Fri, 12 Jun 2015 18:19:27 +0000
From:	"Liang, Kan" <kan.liang@...el.com>
To:	David Ahern <dsahern@...il.com>, Andi Kleen <andi@...stfloor.org>
CC:	Arnaldo Carvalho de Melo <acme@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"Huang, Ying" <ying.huang@...el.com>
Subject: RE: [PATCH 1/1] perf,tools: add time out to force stop endless mmap
 processing


> 
> On 6/12/15 11:05 AM, Liang, Kan wrote:
> >>
> >> On 6/12/15 8:42 AM, Liang, Kan wrote:
> >>>
> >>>>
> >>>> On 6/11/15 12:47 PM, Andi Kleen wrote:
> >>>>>> Can you elaborate on an example? I don't see how this can
> happen
> >>>>>> reading a maps file. And it does not read maps for all threads
> >>>>>> only thread group leaders.
> >>>>>
> >>>>> This is with a stress test case that generates lots of small
> >>>>> mappings at very high speed and frees them again. So the maps file
> >>>>> keeps changing faster than the proc reader can keep it and it can
> >>>>> end up with a live lock.
> >>>>
> >>>> Can you pass it along? I'd like to see how the task_diag proposal
> >>>> handles
> >> it.
> >>>>
> >>>> https://github.com/dsahern/linux/commits/task_diag-wip
> >>>
> >>> Hi David,
> >>>
> >>> I tried the task_diag on my platform, but it shows error message
> >>> when I run perf top. " Message handling failed: rc -1, errno 25".
> >>> And it looks perf top failed to get maps information.
> >>
> >> Not surprising; it's only half-baked. Can you try perf-record? So far
> >> that is the only one I have tested.
> >>
> >
> > Perf record cannot reproduce the infinite loop which found in perf top.
> > But we can observe that synthesized threads took very long time in perf
> record.
> >
> > According to test result as below, current perf cost 13s to read the
> > maps, while task_diag cost 14s to synthesized thread.
> > (Note: The time will increase with the test run.)
> >
> > So it looks task_diag doesn't help on this issue.
> >
> > [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.

> 
> >
> > [perf]$ sudo ./perf_task_diag record -e instructions:pp --pid 14560
> > synthesized threads took 14.435450 sec ^C[ perf record: Woken up 1
> > times to write data ] [ perf record: Captured and wrote 0.035 MB
> > perf.data (885 samples) ]
> >
> >
> >> Also, while running that kernel you can build the test programs under
> >> tools/testing/selftests/task_diag/ and try task_diag_all. I am away
> >> from my dev box at the moment. As I recall you will want to try
> 'task_diag_all o $pid'
> >> or 'task_diag_all a'
> >>
> > Neither options work on my platform.
> >
> > [task_diag]$ sudo ./task_diag_all a
> > Unable to receive message: Operation not supported [task_diag]$ sudo
> > ./task_diag_all o 14751 Unable to receive message: Operation not
> > supported
> 
> Are you sure task_diag is enabled? There is an option under General I
> believe:
> config TASK_DIAG
>          bool "Export task/process properties through netlink"
>          depends on NET && TASKSTATS
>          default n
>          help
>            Export selected properties for tasks/processes through the
>            generic netlink interface. Unlike the proc file system, task_diag
>            returns information in a binary format, allows to specify which
>            information are required.
> 
>            Say N if unsure.
> 
It works now.

Thanks,
Kan

> David

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