linux-kernel - Re: [PATCH 11 of 11] x86: defer cr3 reload when doing pud

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Date:	Fri, 25 Jan 2008 22:03:47 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Andi Kleen <ak@...e.de>
CC:	Ingo Molnar <mingo@...e.hu>, Jeremy Fitzhardinge <jeremy@...p.org>,
	Keir Fraser <Keir.Fraser@...cam.ac.uk>,
	LKML <linux-kernel@...r.kernel.org>,
	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()

Andi Kleen wrote:
> 
>> 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)
> 
> I think it would be an interesting experiment to switch flush_tlb_range()
> over to INVLPG if the length is below some threshold and see if there 
> are visible effects in macro benchmarks. The main problem
> would be to determine the right threshold -- would likely be CPU dependent.
> 

It would be an interesting experiment.  Odds are pretty good that the 
cutover is roughly linear in the TLB size.

	-hpa
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