linux-kernel - Re: [PATCH 2/3] x86/flush_tlb: try flush_tlb_single one by one in flush_tlb

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Date:	Wed, 02 May 2012 21:24:41 +0800
From:	Alex Shi <alex.shi@...el.com>
To:	Nick Piggin <npiggin@...il.com>
CC:	Borislav Petkov <bp@...64.org>, andi.kleen@...el.com,
	tim.c.chen@...ux.intel.com, jeremy@...p.org, chrisw@...s-sol.org,
	akataria@...are.com, tglx@...utronix.de, mingo@...hat.com,
	hpa@...or.com, rostedt@...dmis.org, fweisbec@...il.com,
	riel@...hat.com, luto@....edu, avi@...hat.com, len.brown@...el.com,
	paul.gortmaker@...driver.com, dhowells@...hat.com,
	fenghua.yu@...el.com, yinghai@...nel.org, cpw@....com,
	steiner@....com, linux-kernel@...r.kernel.org,
	yongjie.ren@...el.com
Subject: Re: [PATCH 2/3] x86/flush_tlb: try flush_tlb_single one by one in
 flush_tlb_range

On 05/02/2012 09:04 PM, Nick Piggin wrote:

> On 2 May 2012 21:38, Alex Shi <alex.shi@...el.com> wrote:
>> On 05/02/2012 05:38 PM, Borislav Petkov wrote:
>>
>>> On Wed, May 02, 2012 at 05:24:09PM +0800, Alex Shi wrote:
>>>> For some of scenario, above equation can be modified as:
>>>> (512 - X) * 100ns(assumed TLB refill cost) = X * 140ns(assumed invlpg cost)
> 
> It should not be that optimistic, because that equation assumes every
> unflushed entry saves a TLB refill too.
> 


Yes, it is just ideal scenario to do analysis. In the code, the judgment
depends on the 'active entries' instead of the fixed TLB line number.

active entries = min(this process's page number, TLB line number)

> I think it is always a good idea to make such fundamental primitives
> cheaper though.
> 


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