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Open Source and information security mailing list archives
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Date: Fri, 17 Oct 2008 14:36:56 -0500 From: Christoph Lameter <cl@...ux-foundation.org> To: "Luck, Tony" <tony.luck@...el.com> CC: Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>, Linus Torvalds <torvalds@...ux-foundation.org>, Andrew Morton <akpm@...ux-foundation.org>, Ingo Molnar <mingo@...e.hu>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, "linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>, Steven Rostedt <rostedt@...dmis.org>, Peter Zijlstra <a.p.zijlstra@...llo.nl>, Thomas Gleixner <tglx@...utronix.de>, David Miller <davem@...emloft.net>, Ingo Molnar <mingo@...hat.com>, "H. Peter Anvin" <hpa@...or.com> Subject: Re: [RFC patch 15/15] LTTng timestamp x86 Luck, Tony wrote: > Even one line bouncing between cpus can be a performamce disaster. > You'll probably hit a serious wall somewhere between 8 and 16 > cpus (ia64 has code that looks a lot like this in the gettimeofday() > path because it does not synchronize cpu cycle counters ... some The code exist by necessity because some systems do not have synchronized ITCs and one would not have time go backward. The cmpxchg there is usually switched off. Its horrible in terms of scaling to large numbers of processor and also horrible in terms of clock accuracy. -- 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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