linux-kernel - Re: [PATCH 1/3] stop_machine: short exit path for if we cannot create enough threads

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Date:	Tue, 6 May 2008 12:57:05 +1000
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	Hidetoshi Seto <seto.hidetoshi@...fujitsu.com>
Cc:	linux-kernel@...r.kernel.org,
	Kathy Staples <kathy.staples@....ibm.com>
Subject: Re: [PATCH 1/3] stop_machine: short exit path for if we cannot create enough threads

On Tuesday 29 April 2008 11:29:21 Hidetoshi Seto wrote:
> stop_machine_run() invokes kthread 'kstopmachine' and the kthread
> creates its children for every other cpus.

Hi Hidetoshi,

   I'm glad to see some work on stop_machine!  I'd really like to rewrite it: 
it has some nasty properties at the moment and introduces latency it doesn't 
have to.

Among the properties we want in a new stop_machine are:
1) timeout protection (as your patches),
2) arbitrary cpumask for what cpus to run function on,
3) ability to run something other than cpu_relax() on stopped cpus,
4) much lower latency for the common case,
5) simpler than the current code.

I expect to get to this in the next week or so, but please remind me if you 
don't see anything.  I've applied your patches in the mean time (although #3 
needed to be wrapped in #ifdef CONFIG_STOPMACHINE) in case I don't get that 
work finished for 2.6.27.

Thanks!
Rusty.
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