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Date: Tue, 6 Apr 2010 18:50:31 +0200
From: Andrea Arcangeli <aarcange@redhat.com>
Subject: Re: [PATCH 00 of 41] Transparent Hugepage Support #17
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To: Nick Piggin <npiggin@suse.de>
Cc: Avi Kivity <avi@redhat.com>, 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 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.

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