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Date: Mon, 29 Jun 2009 07:01:23 -0700 From: Arjan van de Ven <arjan@...radead.org> To: Luming Yu <luming.yu@...il.com> Cc: Ingo Molnar <mingo@...e.hu>, LKML <linux-kernel@...r.kernel.org>, suresh.b.siddha@...el.com, venkatesh.pallipadi@...el.com, Thomas Gleixner <tglx@...utronix.de>, "H. Peter Anvin" <hpa@...or.com> Subject: Re: [RFC patch] Use IPI_shortcut for lapic timer broadcast On Mon, 29 Jun 2009 16:43:16 +0800 Luming Yu <luming.yu@...il.com> wrote: > > Even a Pentium-5 100 MHz dual box was able to do cross-CPU IPIs > > within 10-20 microseconds more than a decade ago - so 50-100 usecs > > latency on a modern platform is totally out of this planet and will > > hurt Linux performance big time. And the worst thing about it is > > that none of the usual performance metrics will really show _why_ > > performance is tanking ... > > > > > Please note this is deep-C-state related. > C state does add extra latency.. but I don't know how much... C states normally only add on the "wait for" side, not on the "send" side. (RHEL5 is rather old, so it may have done things a bit different) Maybe it is time for mainline to not allow a !NO_HZ config.... -- 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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