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Open Source and information security mailing list archives
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Date: Sat, 8 Nov 2008 10:41:16 -0800 From: Arjan van de Ven <arjan@...radead.org> To: Linus Torvalds <torvalds@...ux-foundation.org> Cc: Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org, Andrew Morton <akpm@...ux-foundation.org>, Peter Zijlstra <a.p.zijlstra@...llo.nl>, Mike Galbraith <efault@....de> Subject: Re: [git pull] scheduler updates On Sat, 8 Nov 2008 10:28:21 -0800 (PST) Linus Torvalds <torvalds@...ux-foundation.org> wrote: > > > On Sat, 8 Nov 2008, Ingo Molnar wrote: > > > > Ingo Molnar (2): > > sched: improve sched_clock() performance > > sched: optimize sched_clock() a bit > > Btw, why do we do that _idiotic_ rdtsc_barrier() AT ALL? > > No sane user can possibly want it. If you do 'rdtsc', there's nothing > you can do about a few cycles difference due to OoO _anyway_. Adding > barriers is entirely meaningless - it's not going to make the return > value mean anything else. > > Can we please just remove that idiocy? Or can somebody give a _sane_ > argument for it? historically it was for early AMD cpus (K7, not sure if early K8 did this) where 2 consecutive rdtsc's in the same codestream would get reordered compared to eachother, so you could observe the tsc go backwards... -- Arjan van de Ven Intel Open Source Technology Centre For development, discussion and tips for power savings, visit http://www.lesswatts.org -- 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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