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Open Source and information security mailing list archives
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Date: Tue, 03 Apr 2007 17:31:44 -0700 From: "H. Peter Anvin" <hpa@...or.com> To: Ulrich Drepper <drepper@...hat.com> CC: Davide Libenzi <davidel@...ilserver.org>, Linux Kernel <linux-kernel@...r.kernel.org>, Andrew Morton <akpm@...ux-foundation.org> Subject: Re: getting processor numbers Ulrich Drepper wrote: > Davide Libenzi wrote: >> It sucks when seen from a micro-bench POV, but does it really matter >> overall? The vast majority of software usually calls >> sysconf(_SC_NPROCESSORS_*) with very little frequency (mostly once at >> initialization time) anyway. That's what 50us / call? > > This is not today's situation. Yes, 10 years ago when I added the > support to glibc it wasn't much of a problem. But times change. As I > said before in this thread, OpenMP by default scales the number of > threads used for a parallel loops depending on the number of available > processors/cores and therefore the number must be retrieved every time > (with perhaps minimal caching of a few secs, but this requires > gettimeofday calls...). All of a sudden this is not micro benchmark > anymore. It's a real issue which we only became aware of because it is > noticeable in real life. Sounds like it would need a device which can be waited upon for changes. -hpa - 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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