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Date: Wed, 24 Feb 2010 15:57:31 -0500
From: Rik van Riel <riel@redhat.com>
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Subject: Re: [patch 36/36] khugepaged
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To: Andrew Morton <akpm@linux-foundation.org>
Cc: aarcange@redhat.com, linux-mm@kvack.org, Marcelo Tosatti <mtosatti@redhat.com>, Adam Litke <agl@us.ibm.com>, Avi Kivity <avi@redhat.com>, Izik Eidus <ieidus@redhat.com>, Hugh Dickins <hugh.dickins@tiscali.co.uk>, Nick Piggin <npiggin@suse.de>, Mel Gorman <mel@csn.ul.ie>, Dave Hansen <dave@linux.vnet.ibm.com>, Benjamin Herrenschmidt <benh@kernel.crashing.org>, Ingo Molnar <mingo@elte.hu>, 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>
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On 02/24/2010 03:52 PM, Andrew Morton wrote:
> On Wed, 24 Feb 2010 15:28:44 -0500 Rik van Riel<riel@redhat.com>  wrote:
>
>>> Generally it seems like a bad idea to do this sort of thing
>>> asynchronously.  Because it reduces repeatability across runs and
>>> across machines - system behaviour becomes more dependent on the size
>>> of the machine and the amount of activity in unrelated jobs?
>>
>> Isn't system performance already dependent on the size of
>> the machine and the amount of activity in unrelated jobs?
>
> I said "repeatability".
>
>> Using hugepages is a performance enhancement only and
>> otherwise transparent to userspace.
>
> And it's bad that a job run will take a varying amount of CPU time due
> to unrelated activity.  Yes, that can already happen, but it's
> undesirable and it's undesirable to worsen things.
>
> If this work could be done synchronously then runtimes become more
> consistent, which is a good thing.

Only if it means run times become shorter...

I would argue that running consistently slower would
be worse than running inconsitently faster, but maybe
that's just me :)

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