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Date: Fri, 22 Feb 2013 13:11:23 +0100 From: Ingo Molnar <mingo@...nel.org> To: Mike Galbraith <efault@....de> Cc: Peter Zijlstra <a.p.zijlstra@...llo.nl>, Michael Wang <wangyun@...ux.vnet.ibm.com>, LKML <linux-kernel@...r.kernel.org>, Paul Turner <pjt@...gle.com>, Andrew Morton <akpm@...ux-foundation.org>, alex.shi@...el.com, Ram Pai <linuxram@...ibm.com>, "Nikunj A. Dadhania" <nikunj@...ux.vnet.ibm.com>, Namhyung Kim <namhyung@...nel.org> Subject: Re: [RFC PATCH v3 0/3] sched: simplify the select_task_rq_fair() * Mike Galbraith <efault@....de> wrote: > On Fri, 2013-02-22 at 10:54 +0100, Ingo Molnar wrote: > > * Mike Galbraith <efault@....de> wrote: > > > > > On Fri, 2013-02-22 at 09:36 +0100, Peter Zijlstra wrote: > > > > On Fri, 2013-02-22 at 10:37 +0800, Michael Wang wrote: > > > > > But that's really some benefit hardly to be estimate, especially when > > > > > the workload is heavy, the cost of wake_affine() is very high to > > > > > calculated se one by one, is that worth for some benefit we could not > > > > > promise? > > > > > > > > Look at something like pipe-test.. wake_affine() used to > > > > ensure both client/server ran on the same cpu, but then I > > > > think we added select_idle_sibling() and wrecked it again :/ > > > > > > Yeah, that's the absolute worst case for > > > select_idle_sibling(), 100% synchronous, absolutely nothing to > > > be gained by cross cpu scheduling. Fortunately, most tasks do > > > more than that, but nonetheless, select_idle_sibling() > > > definitely is a two faced little b*tch. I'd like to see the > > > evil b*tch die, but something needs to replace it's pretty > > > face. One thing that you can do is simply don't call it when > > > the context switch rate is incredible.. its job is to recover > > > overlap, if you're scheduling near your max, there's no win > > > worth the cost. > > > > Couldn't we make the cutoff dependent on sched_migration_cost? > > If the wakeup comes in faster than that then don't spread. > > No, that's too high, you loose too much of the pretty face. > [...] Then a logical proportion of it - such as half of it? Thanks, Ingo -- 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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