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Date: Sat, 26 Jan 2008 01:11:28 +0100 From: Ingo Molnar <mingo@...e.hu> To: Jeremy Fitzhardinge <jeremy@...p.org> Cc: Keir Fraser <Keir.Fraser@...cam.ac.uk>, "H. Peter Anvin" <hpa@...or.com>, LKML <linux-kernel@...r.kernel.org>, Andi Kleen <ak@...e.de>, Jan Beulich <jbeulich@...ell.com>, Eduardo Pereira Habkost <ehabkost@...hat.com>, Ian Campbell <ijc@...lion.org.uk>, William Irwin <wli@...omorphy.com>, Linus Torvalds <torvalds@...ux-foundation.org> Subject: Re: [PATCH 11 of 11] x86: defer cr3 reload when doing pud_clear() * Jeremy Fitzhardinge <jeremy@...p.org> wrote: > Is there any guide about the tradeoff of when to use invlpg vs > flushing the whole tlb? 1 page? 10? 90% of the tlb? i made measurements some time ago and INVLPG was quite uniformly slow on all important CPU types - on the order of 100+ cycles. It's probably microcode. With a cr3 flush being on the order of 200-300 cycles (plus any add-on TLB miss costs - but those are amortized quite well as long as the pagetables are well cached - which they usually are on today's 2MB-ish L2 caches), the high cost of INVLPG rarely makes it worthwile for anything more than a few pages. so INVLPG makes sense for pagetable fault realated single-address flushes, but they rarely make sense for range flushes. (and that's how Linux uses it) Ingo -- 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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