linux-kernel - Re: [GIT PULL] Re: REGRESSION: Performance regressions from switching anon

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Message-ID: <20110616225803.GA28557@elte.hu>
Date:	Fri, 17 Jun 2011 00:58:03 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Andi Kleen <ak@...ux.intel.com>
Cc:	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Tim Chen <tim.c.chen@...ux.intel.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Hugh Dickins <hughd@...gle.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	David Miller <davem@...emloft.net>,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	Russell King <rmk@....linux.org.uk>,
	Paul Mundt <lethal@...ux-sh.org>,
	Jeff Dike <jdike@...toit.com>,
	Richard Weinberger <richard@....at>,
	Tony Luck <tony.luck@...el.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Mel Gorman <mel@....ul.ie>, Nick Piggin <npiggin@...nel.dk>,
	Namhyung Kim <namhyung@...il.com>, shaohua.li@...el.com,
	alex.shi@...el.com, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, "Rafael J. Wysocki" <rjw@...k.pl>
Subject: Re: [GIT PULL] Re: REGRESSION: Performance regressions from
 switching anon_vma->lock to mutex


* Andi Kleen <ak@...ux.intel.com> wrote:

> > There's a crazy solution for that: the idle thread could process 
> > RCU callbacks carefully, as if it was running user-space code.
> 
> In Ben's kernel NFS server case the system may not be idle.

An always-100%-busy NFS server is very unlikely, but even in the 
hypothetical case a kernel NFS server is really performing system 
calls from a kernel thread in essence. If it doesn't do it explicitly 
then its main loop can easily include a "check RCU callbacks" call.

Thanks,

	Ingo
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