linux-kernel - Re: [PATCH] flush_cpu_workqueue: don't flush an empty ->worklist

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Message-Id: <20070109021551.b7781c53.akpm@osdl.org>
Date:	Tue, 9 Jan 2007 02:15:51 -0800
From:	Andrew Morton <akpm@...l.org>
To:	vatsa@...ibm.com
Cc:	Oleg Nesterov <oleg@...sign.ru>,
	David Howells <dhowells@...hat.com>,
	Christoph Hellwig <hch@...radead.org>,
	Ingo Molnar <mingo@...e.hu>,
	Linus Torvalds <torvalds@...l.org>,
	linux-kernel@...r.kernel.org, Gautham shenoy <ego@...ibm.com>
Subject: Re: [PATCH] flush_cpu_workqueue: don't flush an empty ->worklist

On Tue, 9 Jan 2007 15:39:26 +0530
Srivatsa Vaddagiri <vatsa@...ibm.com> wrote:

> I just hope the latency of freeze_processes() is tolerable ..

It'll be roughly proportional to the number of processes, I guess: if we
have 100,000 processes (or threads) doing sleep(1000000) then yeah, it'll
take some time to wake them all up and capture them in refrigerator().

But I suspect a suitable fix for any problems which arise there is to
implement gang-offlining and onlining, rather than the present
one-cpu-at-a-time.  That'd be pretty simple to do: we already have sysfs
interfaces which take a cpumask.
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