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

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Message-ID: <20150325192009.GZ162412@redhat.com>
Date:	Wed, 25 Mar 2015 15:20:09 -0400
From:	Don Zickus <dzickus@...hat.com>
To:	David Ahern <dsahern@...il.com>
Cc:	Arnaldo Carvalho de Melo <arnaldo.melo@...il.com>,
	Joe Mario <jmario@...hat.com>, linux-kernel@...r.kernel.org,
	Jiri Olsa <jolsa@...hat.com>
Subject: Re: [PATCH] perf tool: Fix ppid for synthesized fork events

On Wed, Mar 25, 2015 at 09:03:38AM -0600, David Ahern wrote:
> On 3/25/15 7:24 AM, Arnaldo Carvalho de Melo wrote:
> >So it starts when there are tons of threads in the system, for which
> >synthezing from /proc will have to take place, without looking again at
> >that patch, I can't think about what would be a problem :-\
> 
> 3 extra lines are read from /proc/pid/status:
> 
> Name:	bash
> State:	S (sleeping)
> Tgid:	6046
> 
> < current patch breaks here>
> 
> Ngid:	0
> Pid:	6046
> PPid:	6045
> 
> < my patch reads these 3 lines, repeats the memcmp and does an atoi
> on the PPid: value >

Ah, I read my email out of order.  So you figured out the extra latency.
Nice.  In that case I think I am ok with your V2, though I still think split
it out would make sense.

Sorry about that.  Thanks for quickly debugging that!!

Cheers,
Don

> 
> Let me remove that loop by reading in 4k at a time and making a
> single pass. That should bring down the overhead, but filling in the
> ppid will add some.
> 
> David
> 
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