linux-kernel - Re: [PATCH v5 6/7] x86/tlb: optimizing flush_tlb

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Message-ID: <CAJRGBZyJy416yeyTgrcBR6b-7Y+cBXiz91f_gscRSado1wQVhg@mail.gmail.com>
Date:	Tue, 15 May 2012 21:27:10 +0800
From:	Luming Yu <luming.yu@...il.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	Nick Piggin <npiggin@...il.com>, Alex Shi <alex.shi@...el.com>,
	tglx@...utronix.de, mingo@...hat.com, hpa@...or.com, arnd@...db.de,
	rostedt@...dmis.org, fweisbec@...il.com, jeremy@...p.org,
	riel@...hat.com, luto@....edu, avi@...hat.com, len.brown@...el.com,
	dhowells@...hat.com, fenghua.yu@...el.com, borislav.petkov@....com,
	yinghai@...nel.org, ak@...ux.intel.com, cpw@....com,
	steiner@....com, akpm@...ux-foundation.org, penberg@...nel.org,
	hughd@...gle.com, rientjes@...gle.com,
	kosaki.motohiro@...fujitsu.com, n-horiguchi@...jp.nec.com,
	tj@...nel.org, oleg@...hat.com, axboe@...nel.dk, jmorris@...ei.org,
	kamezawa.hiroyu@...fujitsu.com, viro@...iv.linux.org.uk,
	linux-kernel@...r.kernel.org, yongjie.ren@...el.com,
	linux-arch@...r.kernel.org, jcm@...masters.org
Subject: Re: [PATCH v5 6/7] x86/tlb: optimizing flush_tlb_mm

On Tue, May 15, 2012 at 9:06 PM, Peter Zijlstra <a.p.zijlstra@...llo.nl> wrote:
> On Tue, 2012-05-15 at 20:58 +0800, Luming Yu wrote:
>>
>>
>> Both __native_flush_tlb() and __native_flush_tlb_single(...)
>> introduced roughly 1 ns  latency to tsc sampling executed in

Fix typo, I just observed 1us with current tool, I would check if I
can push the accuracy to nanoseconds level.

>> stop_machine_context in two logical CPUs
>
> But you have to weight that against the cost of re-population, and

Right, it's hard to detect, but I will try if I can get measurement
done in a simple test tool to help people measure
this kind of stuff in few minutes.

> that's the difficult bit, since we have no clue how many tlb entries are
> in use by the current cr3.
>
> It might be possible for intel to give us this information, I've asked
> for something similar for cachelines.

This is the official document
http://www.intel.com/content/dam/doc/manual/64-ia-32-architectures-optimization-manual.pdf

Let me know if it can answer your question.

>
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