Re: [PATCH 1/1] perf,tools: add time out to force stop endless mmap processing

[David Ahern]

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?


> > 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.

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


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