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Date: Mon, 02 Feb 2009 09:53:38 +0100 From: Peter Zijlstra <peterz@...radead.org> To: "Zhang, Yanmin" <yanmin_zhang@...ux.intel.com> Cc: Lin Ming <ming.m.lin@...el.com>, linux-kernel <linux-kernel@...r.kernel.org> Subject: Re: hackbench [pthread mode] regression with 2.6.29-rc3 On Mon, 2009-02-02 at 09:12 +0800, Zhang, Yanmin wrote: > process timer (by setitimer) isn't good. Is per-cpu itimer to improve it? > So the per-cpu itimer could improve this situation when thread number is far bigger than > cpu number. I didn't retry specweb2005 with 2.6.28. 1) process wide itimers are rubbish, 2) per-cpu itimers are rubbish too, for the very simple reason they waste gobs of memory for sane programs. I would rather go back to the old model where we iterate all threads, and find a way to not make programs with too many threads for their own good lock up the kernel, but instead get poor service. Now the problems appears to be that I overlooked that we keep the itimer clock running at all times, not only when we have a pending timer, and I suppose that the standard mandates that behaviour :/ Anyway, I will try to sort something out, at worst we'll have to revert to the .28 state and live with the per-cpu crap for another release. -- 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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