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

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Message-ID: <CAPa8GCDhGfuYEemdsnUZwh=O6Nco1PH1JgiruvWw3400yz9S8w@mail.gmail.com>
Date:	Wed, 2 May 2012 23:04:51 +1000
From:	Nick Piggin <npiggin@...il.com>
To:	Alex Shi <alex.shi@...el.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 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.

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


>> Also, have you run your patches with other benchmarks beside your
>> microbenchmark, say kernbench, SPEC<something>, i.e. some other
>> multithreaded benchmark touching shared memory? Are you seeing any
>> improvement there?
>
>
> I tested oltp reading and specjbb2005 with openjdk. They should not much
> flush_tlb_range calling. So, no clear improvement.
> Do you know benchmarks which cause enough flush_tlb_range?

x86 does not do such invlpg flushing for munmap either, as far as I
can see?

It would be a little more work to make this happen, but it might show
more benefit, provided glibc does not free too huge chunks at once,
it should apply far more often.
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