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Date: Fri, 14 Sep 2012 15:20:31 -0700 From: Linus Torvalds <torvalds@...ux-foundation.org> To: Peter Zijlstra <a.p.zijlstra@...llo.nl> Cc: Borislav Petkov <bp@...en8.de>, Nikolay Ulyanitsky <lystor@...il.com>, Mike Galbraith <efault@....de>, linux-kernel@...r.kernel.org, Andreas Herrmann <andreas.herrmann3@....com>, Andrew Morton <akpm@...ux-foundation.org>, Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...nel.org> Subject: Re: 20% performance drop on PostgreSQL 9.2 from kernel 3.5.3 to 3.6-rc5 on AMD chipsets - bisected On Fri, Sep 14, 2012 at 3:10 PM, Peter Zijlstra <a.p.zijlstra@...llo.nl> wrote: > > I'm not seeing how it could be. Only ever looking at 1 other cpu > (regardless which one) cannot be the same as checking 'all' of them. Oh, you're right, it has that cpu_idle() in the loop too. So yeah, you can't make it be even remotely equivalent. You can only make it equivalent for the "all other cpu's are idle" case. It doesn't even do *that*, though. In fact, as far as I can tell, it looks like a cpu could be its own idle_buddy. That whole logic looks very odd. I vote we just revert it as "insane". The code really doesn't seem to make any sense. 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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