linux-kernel - Re: [patch 2/2] x86 NMI-safe INT3 and Page Fault

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Message-ID: <20100716154017.GA17970@Krystal>
Date:	Fri, 16 Jul 2010 11:40:17 -0400
From:	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	Avi Kivity <avi@...hat.com>, LKML <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <peterz@...radead.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Steven Rostedt <rostedt@...tedt.homelinux.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Christoph Hellwig <hch@....de>, Li Zefan <lizf@...fujitsu.com>,
	Lai Jiangshan <laijs@...fujitsu.com>,
	Johannes Berg <johannes.berg@...el.com>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Arnaldo Carvalho de Melo <acme@...radead.org>,
	Tom Zanussi <tzanussi@...il.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	akpm@...l.org, "H. Peter Anvin" <hpa@...or.com>,
	Jeremy Fitzhardinge <jeremy@...p.org>,
	"Frank Ch. Eigler" <fche@...hat.com>
Subject: Re: [patch 2/2] x86 NMI-safe INT3 and Page Fault

* Andi Kleen (andi@...stfloor.org) wrote:
> > Well, it seems like all the kernel code calling "vmalloc_sync_all()" (which is
> > much more than perf) can potentially cause large latencies, which could be
> 
> You need to fix all other code too that walks tasks lists to avoid all those.
> 
> % gid for_each_process | wc -l

This can very well be done incrementally. And I agree, these should eventually
targeted too, especially those which hold locks. We've already started hearing
about tasklist lock live-locks in the past year, so I think we're pretty much at
the point where it should be looked at.

Thanks,

Mathieu

> 
> In fact the mm-struct walk is cheaper than a task-list walk because there
> are always less than tasks.

-- 
Mathieu Desnoyers
Operating System Efficiency R&D Consultant
EfficiOS Inc.
http://www.efficios.com
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