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Date: Tue, 22 May 2012 11:01:08 +0200 From: Peter Zijlstra <a.p.zijlstra@...llo.nl> To: Martin Schwidefsky <schwidefsky@...ibm.com> Cc: Ingo Molnar <mingo@...nel.org>, Mike Galbraith <efault@....de>, linux-kernel@...r.kernel.org, Heiko Carstens <heiko.carstens@...ibm.com>, Christian Ehrhardt <ehrhardt@...ux.vnet.ibm.com> Subject: Re: [PATCH 0/2] RFC: readd fair sleepers for server systems On Mon, 2012-05-21 at 17:45 +0200, Martin Schwidefsky wrote: > our performance team found a performance degradation with a recent > distribution update in regard to fair sleepers (or the lack of fair > sleepers). On s390 we used to run with fair sleepers disabled. This change was made a very long time ago.. tell your people to mind what upstream does if they want us to mind them. Also, reports like this make me want to make /debug/sched_features a patch in tip/out-of-tree so that its never available outside development. > We see the performance degradation with our network benchmark and fair > sleepers enabled, the largest hit is on virtual connections: > > VM guest Hipersockets > Throughput degrades up to 18% > CPU load/cost increase up to 17% > VM stream > Throughput degrades up to 15% > CPU load/cost increase up to 22% > LPAR Hipersockets > Throughput degrades up to 27% > CPU load/cost increase up to 20% Why is this, is this some weird interaction with your hypervisor? > In short, we want the fair sleepers tunable back. I understand that on > x86 we want to avoid the cost of a branch on the hot path in place_entity, > therefore add a compile time config option for the fair sleeper control. I'm very much not liking this... this makes s390 schedule completely different from all the other architectures. -- 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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