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Date: Tue, 06 Apr 2010 20:31:24 +0300
From: Avi Kivity <avi@redhat.com>
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Subject: Re: [PATCH 00 of 41] Transparent Hugepage Support #17
References: <20100405232115.GM5825@random.random> <alpine.LFD.2.00.1004051636060.21411@i5.linux-foundation.org> <20100406011345.GT5825@random.random> <alpine.LFD.2.00.1004051836000.5870@i5.linux-foundation.org> <alpine.LFD.2.00.1004051917310.3487@i5.linux-foundation.org> <4BBB052D.8040307@redhat.com> <4BBB2134.9090301@redhat.com> <20100406131024.GA5288@laptop> <4BBB359D.1020603@redhat.com> <20100406134539.GC5288@laptop> <20100406165031.GA5825@random.random>
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To: Andrea Arcangeli <aarcange@redhat.com>
Cc: Nick Piggin <npiggin@suse.de>, Linus Torvalds <torvalds@linux-foundation.org>, Pekka Enberg <penberg@cs.helsinki.fi>, Ingo Molnar <mingo@elte.hu>, Andrew Morton <akpm@linux-foundation.org>, linux-mm@kvack.org, Marcelo Tosatti <mtosatti@redhat.com>, Adam Litke <agl@us.ibm.com>, Izik Eidus <ieidus@redhat.com>, Hugh Dickins <hugh.dickins@tiscali.co.uk>, Rik van Riel <riel@redhat.com>, Mel Gorman <mel@csn.ul.ie>, Dave Hansen <dave@linux.vnet.ibm.com>, Benjamin Herrenschmidt <benh@kernel.crashing.org>, Mike Travis <travis@sgi.com>, KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>, Christoph Lameter <cl@linux-foundation.org>, Chris Wright <chrisw@sous-sol.org>, bpicco@redhat.com, KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>, Balbir Singh <balbir@linux.vnet.ibm.com>, Arnd Bergmann <arnd@arndb.de>, "Michael S. Tsirkin" <mst@redhat.com>, Peter Zijlstra <peterz@infradead.org>, Johannes Weiner <hannes@cmpxchg.org>, Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
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On 04/06/2010 07:50 PM, Andrea Arcangeli wrote:
> On Tue, Apr 06, 2010 at 11:45:39PM +1000, Nick Piggin wrote:
>    
>> problems. Speedups like Linus is talking about would refer to ways to
>> speed up actual workloads, not ways to avoid fundamental limitations.
>>
>> Prefetching, memory parallelism, caches. It's worked for 25 years :)
>>      
> This will always give you a worst case additional 6% on top (gcc is a
> definitive worst case) of all other speedup of the actual workloads,
> for server loads more likely>=15% boost. It's plain underclocking
> your CPU not to run this.
>    

I don't think gcc is worst case.  Workloads that benefit from large 
pages are those with bloated working sets that do a lot of pointer 
chasing and do little computation in between.  gcc fits two out of three 
(just a partial score on the first).

-- 
Do not meddle in the internals of kernels, for they are subtle and quick to panic.

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