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Date: Wed, 9 Jan 2008 21:40:28 +0100 From: Andi Kleen <andi@...stfloor.org> To: Arjan van de Ven <arjan@...radead.org> Cc: Andi Kleen <andi@...stfloor.org>, Ingo Molnar <mingo@...e.hu>, tglx@...utronix.de, linux-kernel@...r.kernel.org, "H. Peter Anvin" <hpa@...or.com> Subject: Re: More breakage in native_rdtsc out of line in git-x86 On Wed, Jan 09, 2008 at 12:25:59PM -0800, Arjan van de Ven wrote: > On Wed, 9 Jan 2008 18:48:00 +0100 > > And after all that's still by far the most common system call > > (not only for databases; i profiled this using systemtap in some > > loads some time ago and it usually came up with >50%) > > and quite important for many workloads. > > > > btw be careful with this; the X server uses gettimeofday in it's equivalent of udelay()... > (and we all know how useful it is to make the delay loops faster ;-) People tend to make jokes about optimizing the idle loop too, but they're actually wrong. Exit latency for the idle loop is important -- it decides how quickly you can react to load changes on idle CPUs. For short udelays I suspect shorter exit latency is also moderately useful. But anyways there are plenty of gtod users outside the X server. e.g. common not user space case is packet timestamps. -Andi -- 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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