linux-kernel - Re: [PATCH v2] perf tool: Fix ppid for synthesized fork events

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Date:	Wed, 25 Mar 2015 13:55:44 -0600
From:	David Ahern <dsahern@...il.com>
To:	Don Zickus <dzickus@...hat.com>
CC:	acme@...nel.org, linux-kernel@...r.kernel.org,
	Joe Mario <jmario@...hat.com>, Jiri Olsa <jolsa@...hat.com>
Subject: Re: [PATCH v2] perf tool: Fix ppid for synthesized fork events

On 3/25/15 1:15 PM, Don Zickus wrote:
> On Wed, Mar 25, 2015 at 10:51:10AM -0600, David Ahern wrote:
>> 363b785f38 added synthesized fork events and set a thread's parent id
>> to itself. Since we are already processing /proc/<pid>/status the ppid
>> can be determined properly. Make it so.
>>
>> Performance impact measured on a sparc based T5-8 (1024 CPUs):
>> $ ps -efL | wc -l
>> 20185
>>
>> Current code:
>> $ time perf record -o perf-no-ppid.data -e cpu-clock -F 1000 -a -v -BN -- usleep 1
>> mmap size 532480B
>> [ perf record: Woken up 0 times to write data ]
>> failed to write feature 9
>> [ perf record: Captured and wrote 0.000 MB perf-no-ppid.data ]
>>
>> real	0m26.144s
>> user	0m0.452s
>> sys	0m25.564s
>>
>> With PPID patch:
>> $ time ./perf_ppid record -o perf-ppid.data -e cpu-clock -F 1000 -a -v -BN -- usleep 1
>> mmap size 532480B
>> [ perf record: Woken up 0 times to write data ]
>> failed to write feature 9
>> [ perf record: Captured and wrote 0.000 MB perf-ppid.data ]
>>
>> real	0m25.743s
>> user	0m0.268s
>> sys	0m25.368s
>>
>> Signed-off-by: David Ahern <dsahern@...il.com>
>> Cc: Don Zickus <dzickus@...hat.com>
>> Cc: Joe Mario <jmario@...hat.com>
>> Cc: Jiri Olsa <jolsa@...hat.com>
>> ---
>> v2:
>> - removed loop in place of 1 read and processing a buffer
>
> Hmm, I am not entirely sure this is correct.  You made an optimization that
> hides the negative impact your patch does.  I would prefer you split this
> patch into two pieces.  One with the read loop optimization (which I think
> is great) and the second is your ppid change.
>
> I would then like to redo our test with the first patch applied and then
> both patches applied.
>

 From your other response I take it you understand the patch now? It is 
a matter of semantics to break this single into 2 -- optimize the 
existing code and then add the ppid. End result will be what this patch 
shows. Before I do that can you /Joe confirm the performance is acceptable?

Thanks,

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