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

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Message-ID: <20091118213355.GA16630@srcf.ucam.org>
Date:	Wed, 18 Nov 2009 21:33:55 +0000
From:	Matthew Garrett <mjg59@...f.ucam.org>
To:	Kay Sievers <kay.sievers@...y.org>
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 10:06:33PM +0100, Kay Sievers wrote:

> That's true, but I think there is a significant difference between
> polling every one or two seconds for media changes, and usually one or
> two minutes for a disk idle. It's not that we poll in a rather hight
> frequency, in an arbitrary interval, and check if some condition is
> met.

My use cases are on the order of a second.

> I still don't think that we should add new event interfaces which are
> single-subscriber only, and use global values for a specific user.
> What if there will be another independent user for this, which might
> want a different timeout? They fight over the trigger value to set in
> sysfs?

You can trivially multiplex without any additional wakeups. Something 
like devkit-disks can simply trigger on the lowest requested time and 
then schedule wakeups for subscribers who want a different timeout.

> From my perspective, the once-at-timeout wakeup is more acceptable
> than an in-kernel policy setting for a single-subscriber event
> interface.

I'd be open to it being something for multiple subscribers, though that 
would add to the complexity in the block code and I'm not sure that's 
needed.

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