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Date: Wed, 23 Dec 2009 12:48:51 +0900 From: Tejun Heo <tj@...nel.org> To: Peter Zijlstra <peterz@...radead.org> CC: torvalds@...ux-foundation.org, awalls@...ix.net, linux-kernel@...r.kernel.org, jeff@...zik.org, mingo@...e.hu, akpm@...ux-foundation.org, jens.axboe@...cle.com, rusty@...tcorp.com.au, cl@...ux-foundation.org, dhowells@...hat.com, arjan@...ux.intel.com, avi@...hat.com, johannes@...solutions.net, andi@...stfloor.org Subject: Re: workqueue thing Hello, On 12/22/2009 08:04 PM, Peter Zijlstra wrote: > On Tue, 2009-12-22 at 08:50 +0900, Tejun Heo wrote: >>> Also, I think that whole move tasks back on online stuff is utter crazy, >>> just move then to another cpu and leave them there. >> >> Can you be more specific? Why is it crazy when moving to online but >> !active cpu is necessary anyway? > > because its extra (and above all ugly code) that serves no purpose what > so ever. The forward progress guarantee requires rescuers to migrate to online but !active CPUs during CPU_DOWN_PREPARE, so the only extra code necessary for migrating back remaining workers when a CPU comes back online is the code to actually do that. That's only a couple tens of lines of code in the trustee thread. Now, the other option would to leave those unbound workers alone and make sure they don't take up new works once new CPUs come online which would require code in hotter path and results in less consistent behavior. The tradeoff seems pretty obvious to me. Doesn't it? Thanks. -- tejun -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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