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

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Date:	Fri, 12 Jun 2015 13:29:13 -0600
From:	David Ahern <dsahern@...il.com>
To:	"Liang, Kan" <kan.liang@...el.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 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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