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Date: Wed, 18 Nov 2009 21:45:06 +0000
From: Matthew Garrett <mjg59@srcf.ucam.org>
To: Kay Sievers <kay.sievers@vrfy.org>
Cc: David Zeuthen <david@fubar.dk>, linux-kernel@vger.kernel.org,
       axboe@kernel.dk, linux-hotplug@vger.kernel.org
Subject: Re: [PATCH] [RFC] Add support for uevents on block device idle
	changes
Message-ID: <20091118214506.GA17019@srcf.ucam.org>
References: <ac3eb2510911181130l6f25642cy1d5332f79a112cf9@mail.gmail.com> <20091118194053.GB12944@srcf.ucam.org> <ac3eb2510911181147ufeacb58u5194b0e1e5fd86d6@mail.gmail.com> <20091118195342.GA13627@srcf.ucam.org> <ac3eb2510911181203r1be5c3dajdacec94f196d550c@mail.gmail.com> <20091118200712.GA14026@srcf.ucam.org> <ac3eb2510911181306g221e8940xfbcf8b8e7fa9a56e@mail.gmail.com> <ac3eb2510911181329v26c334a3oab9c554ec64ad0d5@mail.gmail.com> <20091118213526.GB16630@srcf.ucam.org> <ac3eb2510911181339q616c56f7rd31b93caed0286c5@mail.gmail.com>
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On Wed, Nov 18, 2009 at 10:39:26PM +0100, Kay Sievers wrote:
> On Wed, Nov 18, 2009 at 22:35, Matthew Garrett <mjg59@srcf.ucam.org> wrote:
> > On Wed, Nov 18, 2009 at 10:29:23PM +0100, Kay Sievers wrote:
> >
> >> I guess, the "idle_since" file could be made poll()able, and throw an
> >> event when the idle time is re-set to 0, so the value checking needs
> >> only to happen as long we wait for the disk to become idle. As long as
> >> it's busy anyway, the rare wakeups should not matter much. :)
> >
> > That'd be a userspace wakeup every time something gets submitted to the
> > block device, which sounds far from ideal...
> 
> No, you would only poll() when you reached the timeout and the disk
> entered the idle state. This can not happen more frequently than the
> timeout itself.

I don't understand. idle_since would be reset on every access to the 
block device. The alternative is to generate an event when the disk goes 
idle, but that goes back to requiring a timer in the kernel...

-- 
Matthew Garrett | mjg59@srcf.ucam.org
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