linux-kernel - Re: [PATCH RESEND 0/1] AHCI: Optimize interrupt processing

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Date:	Sat, 13 Sep 2014 13:46:30 +0900
From:	Tejun Heo <tj@...nel.org>
To:	Alexander Gordeev <agordeev@...hat.com>
Cc:	linux-kernel@...r.kernel.org, linux-ide@...r.kernel.org
Subject: Re: [PATCH RESEND 0/1] AHCI: Optimize interrupt processing

Hello,

On Thu, Sep 11, 2014 at 02:42:49PM +0200, Alexander Gordeev wrote:
> As conversion of libata to blk mq has long done I tried the change

Hmmm?  You mean scsi-mq?

> against the recent version and the results still appear worthwhile.
> 
> The numbers are taken by running 'dd if=/dev/sd{a,b} of=/dev/null'
> in parallel. All time values are in us.
> 
> Before this update host lock average holdtime was 2.45 and
> average waittime was 1.24. After the update average holdtime
> dropped to 0.29 (about eight times) while average waittime
> decreased to 0.58 (about two times).
> 
> Also, port events are handled with local interrupts enabled
> and compete on individual per-port locks with average holdtime
> 1.25 and average waittime 1.48. So combined average holdtime
> spent while holding host and port locks decreased from 2.45 to
> 0.29 + 1.25 = 1.54 (about 1.6 times).
> 
> The downside of this change is introduction of a kernel thread.

That shouldn't matter at all but can you please present the
information in a more digestable form?  e.g. CPU usage decreased from
A to B when transferring N MB/s on certain setup.

Thanks.

-- 
tejun
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