linux-kernel - Re: [patch] Give kjournald a IOPRIO_CLASS

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Message-ID: <473DC496.6010805@hp.com>
Date:	Fri, 16 Nov 2007 11:25:58 -0500
From:	"Alan D. Brunelle" <alan.brunelle@...com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Rik van Riel <riel@...hat.com>, arjan@...radead.org,
	jens.axboe@...cle.com, mingo@...e.hu, linux-kernel@...r.kernel.org
Subject: Re: [patch] Give kjournald a IOPRIO_CLASS_RT io priority

Here are the results for the latest tests, some notes:

o  The machine actually has 8GiB of RAM, so the tests still may end up 
using (some) page cache. (But at least it was the same for both kernels! 
:-) )

o  Sorry the results took so long - the updated tree size caused the 
runs to take > 12 hours...

o  The longer runs seemed to bring down the standard deviation a bit, 
although they are still quite large.

o  10 runs per test (read large file, read a tree, overwrite large 
file), with averages presented.

o  1st 4 columns (min, avg, max, std dev) refer to the average run 
lengths for the tests - real time, in seconds

o  The last 3 columns are extracted from iostat results over the course 
of the whole run.

o  The read a tree test certainly stands out - the other 2 large file 
manipulations have the two kernels within a couple of percent, but the 
read a tree test has Arjan's patch taking about 47%(!) longer on 
average. The increased %iowait & %system time in all 3 cases is interesting.

Read large file:

Kernel  Min    Avg    Max   Std Dev    %user  %system  %iowait
--------------------------------------------------------------
base :  201.6  215.1  275.5   22.8     0.26%    4.69%   33.54%
arjan:  198.0  210.3  261.5   18.5     0.33%   10.24%   54.00%

Read a tree:

Kernel  Min    Avg    Max   Std Dev    %user  %system  %iowait
--------------------------------------------------------------
base : 3518.2 4631.3 5991.3  784.6     0.19%    3.29%   23.56%
arjan: 5731.6 6849.8 7777.4  731.6     0.32%    9.90%   52.70%

Overwrite large file:

Kernel  Min    Avg    Max   Std Dev    %user  %system  %iowait
--------------------------------------------------------------
base :  104.2  147.7  239.5   38.4      0.02%    0.05%   1.08%
arjan:  106.2  149.7  239.2   38.4      0.25%    0.79%  14.97%

Let me know if there is anything else I can do to elaborate, or if you 
have suggestions for further testing.

Alan
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