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

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Date:	Wed, 18 Nov 2009 20:47:37 +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 Wed, Nov 18, 2009 at 20:40, Matthew Garrett <mjg@...hat.com> wrote:
> On Wed, Nov 18, 2009 at 08:30:07PM +0100, Kay Sievers wrote:
>
>> Wouldn't it be good enough, if we add a file "idle_since" which
>> contains the time of the actual disk idle time, and userspace can
>> schedule a re-examination of that value at the actual end of the idle
>> time it is looking for?
>
> That would require either polling or waking up a userspace application
> on every disk access. Doing it in-kernel involves only a single timer
> wakeup for every active/idle transition.

How would it? If you look for, like a 60 seconds timeout, and the file
contains 20, you schedule a wakeup in 40 seconds. If the file after
the 40 seconds contains 60, you reached your idle timeout exactly at
that moment, if it's less, then you re-calculate and start from the
beginning.

Kay
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