linux-kernel - Re: [PATCH/RFC 12/16] perf tools: Reduce lock contention when processing events

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Date:	Tue, 15 Dec 2015 11:03:32 +0900
From:	Namhyung Kim <namhyung@...nel.org>
To:	Jiri Olsa <jolsa@...hat.com>
Cc:	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	LKML <linux-kernel@...r.kernel.org>,
	David Ahern <dsahern@...il.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Andi Kleen <andi@...stfloor.org>,
	Stephane Eranian <eranian@...gle.com>,
	Adrian Hunter <adrian.hunter@...el.com>
Subject: Re: [PATCH/RFC 12/16] perf tools: Reduce lock contention when
 processing events

Hi Jiri,

On Mon, Dec 14, 2015 at 09:43:04AM +0100, Jiri Olsa wrote:
> On Thu, Dec 10, 2015 at 04:53:31PM +0900, Namhyung Kim wrote:
> > When multi-thread is enabled, the machine->threads_lock is contented
> > as all worker threads try to grab the writer lock using the
> > machine__findnew_thread().  Usually, the thread they're looking for is
> > in the tree so they only need the reader lock though.
> > 
> > Thus try machine__find_thread() first, and then fallback to the
> > 'findnew' API.  This will improve the performance.
> 
> found one other place, but I guess you chose those
> based on profiling the contention?

I only profiled my earlier perf report patchset and found
machine__findnew_thread() in perf_event__preprocess_sample() was
contended.  But perf-report serialized meta events and only process
sample events parallelly.

As perf-top processes all events parallelly, I thought I should use
the same technique for other places.

> 
> parent lookup in machine__process_fork_event

I'll add that too.

Thanks,
Namhyung
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