linux-kernel - Re: [PATCH] [RFC] Add support for uevents on block device idle changes

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Message-ID: <ac3eb2510911190529p6810508fve4941f3077dfd3d9@mail.gmail.com>
Date:	Thu, 19 Nov 2009 14:29:29 +0100
From:	Kay Sievers <kay.sievers@...y.org>
To:	Matthew Garrett <mjg@...hat.com>
Cc:	David Zeuthen <david@...ar.dk>, linux-kernel@...r.kernel.org,
	axboe@...nel.dk, linux-hotplug@...r.kernel.org
Subject: Re: [PATCH] [RFC] Add support for uevents on block device idle 
	changes

On Thu, Nov 19, 2009 at 14:01, Matthew Garrett <mjg@...hat.com> wrote:
> On Thu, Nov 19, 2009 at 12:09:30PM +0100, Kay Sievers wrote:
>> On Wed, Nov 18, 2009 at 22:33, Matthew Garrett <mjg59@...f.ucam.org> wrote:
>> > My use cases are on the order of a second.
>>
>> Ok, what's the specific use case, which should be triggered after a
>> second? I thought you were thinking about disk spindown or similar.
>
> The first is altering ALPM policy. ALPM will be initiated by the host if
> the number of queued requests hits zero - if there's no hysteresis
> implemented, then that can result in a significant performance hit. We
> don't need /much/ hysteresis, but it's the difference between a 50%
> performance hit and not having that.

Can't that logic live entirely in the kernel, instead of being a
rather generic userspace event interface (with the current limitation
to a single user)?

Kay
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