linux-kernel - Re: [RFC 0/4]x86: allocate up to 32 tlb invalidate vectors

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Date:	Mon, 15 Nov 2010 09:53:55 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Shaohua Li <shaohua.li@...el.com>
CC:	lkml <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...e.hu>,
	Andi Kleen <andi@...stfloor.org>
Subject: Re: [RFC 0/4]x86: allocate up to 32 tlb invalidate vectors

On 11/15/2010 06:02 AM, Shaohua Li wrote:
> On Wed, 2010-11-03 at 14:44 +0800, Shaohua Li wrote:
>> Hi,
>> In workload with heavy page reclaim, flush_tlb_page() is frequently
>> used. We currently have 8 vectors for tlb flush, which is fine for small
>> machines. But for big machines with a lot of CPUs, the 8 vectors are
>> shared by all CPUs and we need lock to protect them. This will cause a
>> lot of lock contentions. please see the patch 3 for detailed number of
>> the lock contention.
>> Andi Kleen suggests we can use 32 vectors for tlb flush, which should be
>> fine for even 8 socket machines. Test shows this reduces lock contention
>> dramatically (see patch 3 for number).
>> One might argue if this will waste too many vectors and leave less
>> vectors for devices. This could be a problem. But even we use 32
>> vectors, we still leave 78 vectors for devices. And we now have per-cpu
>> vector, vector isn't scarce any more, but I'm open if anybody has
>> objections.
>>
> Hi Ingo & hpa, any comments about this series?
> 

Hi Shaohua,

It looks good... I need to do a more thorough review and put it in; I
just have been consumed a bit too much by a certain internal project.

	-hpa

-- 
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel.  I don't speak on their behalf.

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