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Message-ID: <45A57333.6060904@yahoo.com.au>
Date: Thu, 11 Jan 2007 10:13:55 +1100
From: Nick Piggin <nickpiggin@yahoo.com.au>
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To: David Chinner <dgc@sgi.com>
CC: Christoph Lameter <clameter@sgi.com>, linux-kernel@vger.kernel.org,
       linux-mm@kvack.org
Subject: Re: [REGRESSION] 2.6.19/2.6.20-rc3 buffered write slowdown
References: <20070110223731.GC44411608@melbourne.sgi.com> <Pine.LNX.4.64.0701101503310.22578@schroedinger.engr.sgi.com> <20070110230855.GF44411608@melbourne.sgi.com>
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David Chinner wrote:
> On Wed, Jan 10, 2007 at 03:04:15PM -0800, Christoph Lameter wrote:
> 
>>On Thu, 11 Jan 2007, David Chinner wrote:
>>
>>
>>>The performance and smoothness is fully restored on 2.6.20-rc3
>>>by setting dirty_ratio down to 10 (from the default 40), so
>>>something in the VM is not working as well as it used to....
>>
>>dirty_background_ratio is left as is at 10?
> 
> 
> Yes.
> 
> 
>>So you gain performance by switching off background writes via pdflush?
> 
> 
> Well, pdflush appears to be doing very little on both 2.6.18 and
> 2.6.20-rc3. In both cases kswapd is consuming 10-20% of a CPU and
> all of the pdflush threads combined (I've seen up to 7 active at
> once) use maybe 1-2% of cpu time. This occurs regardless of the
> dirty_ratio setting.

Hi David,

Could you get /proc/vmstat deltas for each kernel, to start with?

I'm guessing CPU time isn't a problem, but if it is then I guess
profiles as well.

Thanks,
Nick

-- 
SUSE Labs, Novell Inc.
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