Date: Fri, 16 Jul 2010 11:40:17 -0400
From: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
To: Andi Kleen <andi@firstfloor.org>
Cc: Avi Kivity <avi@redhat.com>, LKML <linux-kernel@vger.kernel.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Andrew Morton <akpm@linux-foundation.org>, Ingo Molnar <mingo@elte.hu>,
        Peter Zijlstra <peterz@infradead.org>,
        Steven Rostedt <rostedt@goodmis.org>,
        Steven Rostedt <rostedt@rostedt.homelinux.com>,
        Frederic Weisbecker <fweisbec@gmail.com>,
        Thomas Gleixner <tglx@linutronix.de>, Christoph Hellwig <hch@lst.de>,
        Li Zefan <lizf@cn.fujitsu.com>, Lai Jiangshan <laijs@cn.fujitsu.com>,
        Johannes Berg <johannes.berg@intel.com>,
        Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>,
        Arnaldo Carvalho de Melo <acme@infradead.org>,
        Tom Zanussi <tzanussi@gmail.com>,
        KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>, akpm@osdl.org,
        "H. Peter Anvin" <hpa@zytor.com>,
        Jeremy Fitzhardinge <jeremy@goop.org>,
        "Frank Ch. Eigler" <fche@redhat.com>
Subject: Re: [patch 2/2] x86 NMI-safe INT3 and Page Fault
Message-ID: <20100716154017.GA17970@Krystal>
References: <20100714154923.947138065@efficios.com> <20100714155804.252253097@efficios.com> <4C405078.20707@redhat.com> <20100716144927.GA22516@Krystal> <20100716153433.GA7338@basil.fritz.box>
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* Andi Kleen (andi@firstfloor.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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