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

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Message-ID: <CAPa8GCBaQhksvVT9DAgwzPPkCMrhcYnSdCtUHEe=cQS8_Cm7DQ@mail.gmail.com>
Date:	Tue, 15 May 2012 19:52:58 +1000
From:	Nick Piggin <npiggin@...il.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	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
Subject: Re: [PATCH v5 6/7] x86/tlb: optimizing flush_tlb_mm

On 15 May 2012 19:18, Peter Zijlstra <a.p.zijlstra@...llo.nl> wrote:
> On Tue, 2012-05-15 at 19:15 +1000, Nick Piggin wrote:
>> So this should go to linux-arch...
>>
>> On 15 May 2012 18:55, Alex Shi <alex.shi@...el.com> wrote:
>> > Not every flush_tlb_mm execution moment is really need to evacuate all
>> > TLB entries, like in munmap, just few 'invlpg' is better for whole
>> > process performance, since it leaves most of TLB entries for later
>> > accessing.
>> >
>> > This patch is changing flush_tlb_mm(mm) to flush_tlb_mm(mm, start, end)
>> > in cases.
>>
>> What happened with Peter's comment about using flush_tlb_range for this?
>>
>> flush_tlb_mm() API should just stay unchanged AFAIKS.
>>
>> Then you need to work out the best way to give range info to the tlb/mmu gather
>> API. Possibly passing in the rage for that guy is OK, which x86 can
>> then implement
>> as flush range.
>
> Right, most archs that have tlb_flush_range() do range tracking in
> mmu_gather. Our TLB ops fully support that, there's absolutely no need
> to go change the interface for thos.

It could be warranted to change tlb_flush_mmu to a range API to
avoid doing the per-entry tracking which those architectures do?

The callers have range available easily, so ignoring those could be
noop for generic helpers.
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