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

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Message-id: <4127129.ClfhyhZXo5@amdc1032>
Date:	Thu, 11 Sep 2014 15:36:31 +0200
From:	Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>
To:	Alexander Gordeev <agordeev@...hat.com>
Cc:	Tejun Heo <tj@...nel.org>, linux-kernel@...r.kernel.org,
	linux-ide@...r.kernel.org
Subject: Re: [PATCH RESEND 0/1] AHCI: Optimize interrupt processing


Hi,

On Thursday, September 11, 2014 02:42:49 PM Alexander Gordeev wrote:

> 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.
> 
> The upside is shorter access time to port locks and moving port
> interrupts handling out of the hardware interrupt context.

IMHO it would be great to put the above results into the patch
description (it now looks a bit skimpy).

Best regards,
--
Bartlomiej Zolnierkiewicz
Samsung R&D Institute Poland
Samsung Electronics

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