Messages in this thread | | | Date | Sat, 26 Jan 2008 01:11:28 +0100 | From | Ingo Molnar <> | Subject | Re: [PATCH 11 of 11] x86: defer cr3 reload when doing pud_clear() |
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* Jeremy Fitzhardinge <jeremy@goop.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
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