linux-kernel - RE: [patch 2/2] reduce tlb/cache flush times of agpgart memory allocation

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Date:	Mon, 18 Aug 2008 09:21:12 +0800
From:	"Li, Shaohua" <shaohua.li@...el.com>
To:	Arjan van de Ven <arjan@...radead.org>, Ingo Molnar <mingo@...e.hu>
CC:	lkml <linux-kernel@...r.kernel.org>,
	"airlied@...ux.ie" <airlied@...ux.ie>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...hat.com>,
	"Siddha, Suresh B" <suresh.b.siddha@...el.com>,
	"Pallipadi, Venkatesh" <venkatesh.pallipadi@...el.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>
Subject: RE: [patch 2/2] reduce tlb/cache flush times of agpgart memory
 allocation



>-----Original Message-----
>From: Arjan van de Ven [mailto:arjan@...radead.org]
>Sent: Friday, August 15, 2008 10:41 PM
>To: Ingo Molnar
>Cc: Li, Shaohua; lkml; airlied@...ux.ie; Andrew Morton; Ingo Molnar; Siddha,
>Suresh B; Pallipadi, Venkatesh; Thomas Gleixner; H. Peter Anvin
>Subject: Re: [patch 2/2] reduce tlb/cache flush times of agpgart memory
>allocation
>
>On Fri, 15 Aug 2008 16:31:31 +0200
>Ingo Molnar <mingo@...e.hu> wrote:
>
>>
>> * Shaohua Li <shaohua.li@...el.com> wrote:
>>
>> > To reduce tlb/cache flush, makes agp memory allocation do one flush
>> > after all pages in a region are changed to uc.
>> >
>> > All agp drivers except agp-sgi uses agp_generic_alloc_page() for
>> > .agp_alloc_page, so the patch should work for them. agp-sgi is only
>> > for ia64, so not a problem too.
>>
>> applied to tip/x86/pat - thanks!
>>
>> I've Cc:-ed more PAT folks - any objections?
>>
>
>it really needs something else instead; it needs airlied's array
>allocator
>otherwise you hit the second wall as well (the pat checks per page)
Somebody should have a measurement. In my test, the real bottleneck is the cache flush. It appears flush cache page is slow if there are a lot of pages, In my patch, I use a wbinvd. This can be optimized to do wbinvd with a threshold. Maybe airlied can change his patch with this way.

Thanks,
Shaohua
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