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Date: Wed, 19 Sep 2007 12:39:11 -0700 (PDT) From: Linus Torvalds <torvalds@...ux-foundation.org> To: Ingo Molnar <mingo@...e.hu> cc: Chuck Ebbert <cebbert@...hat.com>, Antoine Martin <antoine@...afix.co.uk>, Satyam Sharma <satyam.sharma@...il.com>, Linux Kernel Development <linux-kernel@...r.kernel.org>, Peter Zijlstra <a.p.zijlstra@...llo.nl> Subject: Re: CFS: some bad numbers with Java/database threading [FIXED] On Wed, 19 Sep 2007, Ingo Molnar wrote: > > Linus, what do you think? I have no strong feelings, I think the patch > cannot hurt (it does not change anything by default) - but we should not > turn the workaround flag on by default. I disagree. I think CFS made "sched_yield()" worse, and what you call "bug workaround" is likely the *better* behaviour. The fact is, sched_yield() is not - and should not be - about "recalculating the position in the scheduler queue" like you do now in CFS. It very much is about moving the thread *dead last* within its priority group. That's what it does for round-robin, and it's not about fairness, it's about - Opengroup: DESCRIPTION The sched_yield() function forces the running thread to relinquish the processor until it again becomes the head of its thread list. It takes no arguments. - Linux man-page: DESCRIPTION A process can relinquish the processor voluntarily without blocking by calling sched_yield. The process will then be moved to the end of the queue for its static priority and a new process gets to run. and quite frankly, the current CFS behaviour simply looks buggy. It should simply not move it to the "right place" in the rbtree. It should move it *last*. Linus - 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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