linux-kernel - Re: [RFC] Block IO Controller V2

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Date:	Mon, 16 Nov 2009 17:18:27 -0500
From:	Vivek Goyal <vgoyal@...hat.com>
To:	"Alan D. Brunelle" <Alan.Brunelle@...com>
Cc:	linux-kernel@...r.kernel.org, jens.axboe@...cle.com
Subject: Re: [RFC] Block IO Controller V2 - some results

On Mon, Nov 16, 2009 at 03:51:00PM -0500, Alan D. Brunelle wrote:

[..]
> ::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::
> 
> The next thing to look at is to see what the "penalty" is for the
> additional code: see how much bandwidth we lose for the capability
> added. Here we see the sum of the system's throughput for the various
> tests:
> 
> ---- ---- - ----------- ----------- ----------- ----------- 
> Mode RdWr N    base       ioc off   ioc no idle  ioc idle   
> ---- ---- - ----------- ----------- ----------- ----------- 
>  rnd   rd 2        17.3        17.1         9.4         9.1 
>  rnd   rd 4        27.1        27.1         8.1         8.2 
>  rnd   rd 8        37.1        37.1         6.8         7.1 
> 

Hi Alan,

This seems to be the most notable result in terms of performance degradation.

I ran two random readers on a locally attached SATA disk. There in fact
I gain in terms of performance because we perform less number of seeks
now as we allocate a continous slice to one group and then move onto
next group.

But in your setup it looks like there is a striped set of disks and seek
cost is less and waiting per group for sync-noidle workload is hurting
instead.

One simple way to test that would be to set slice_idle=0 so that CFQ does
not try to do any idling at all. Can you please re-run above test. This
will help in figuring out whether above performance regression is coming
from idling on sync-noidle workload group per cgroup or not.

Above numbers are in what units?

Thanks
Vivek
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