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Subject: Re: REGRESSION: Performance regressions from switching anon_vma->lock to mutex
From: Linus Torvalds <torvalds@linux-foundation.org>
Date: Wed, 15 Jun 2011 13:55:25 -0700
To: Ingo Molnar <mingo@elte.hu>, Andrew Morton <akpm@linux-foundation.org>
CC: Peter Zijlstra <peterz@infradead.org>,
        Paul McKenney <paulmck@linux.vnet.ibm.com>,
        Tim Chen <tim.c.chen@linux.intel.com>, Hugh Dickins <hughd@google.com>,
        KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        David Miller <davem@davemloft.net>,
        Martin Schwidefsky <schwidefsky@de.ibm.com>,
        Russell King <rmk@arm.linux.org.uk>, Paul Mundt <lethal@linux-sh.org>,
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        Tony Luck <tony.luck@intel.com>,
        KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>,
        Mel Gorman <mel@csn.ul.ie>, Nick Piggin <npiggin@kernel.dk>,
        Namhyung Kim <namhyung@gmail.com>, ak@linux.intel.com,
        shaohua.li@intel.com, alex.shi@intel.com, linux-kernel@vger.kernel.org,
        linux-mm@kvack.org, "Rafael J. Wysocki" <rjw@sisk.pl>
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Ingo Molnar <mingo@elte.hu> wrote:
>
>perf record -g will go a long way towards such a tool already - but i 
>think it would be useful to create a more top-alike view as well. 

perf record -g doesn't help when the issue is that we're recording a single process and the actual work is being done in another unrelated process that is just being woken up.

Sure, you can do a system wide recording, but that shows all kinds of unrelated noise and requires root permissions.

So those rcu threads really need to go.

      Linus