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From: Kay Sievers <kay.sievers@vrfy.org>
Date: Wed, 18 Nov 2009 22:06:33 +0100
Message-ID: <ac3eb2510911181306g221e8940xfbcf8b8e7fa9a56e@mail.gmail.com>
Subject: Re: [PATCH] [RFC] Add support for uevents on block device idle 
	changes
To: Matthew Garrett <mjg59@srcf.ucam.org>
Cc: David Zeuthen <david@fubar.dk>, linux-kernel@vger.kernel.org,
       axboe@kernel.dk, linux-hotplug@vger.kernel.org
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On Wed, Nov 18, 2009 at 21:07, Matthew Garrett <mjg59@srcf.ucam.org> wrote:
> On Wed, Nov 18, 2009 at 09:03:21PM +0100, Kay Sievers wrote:
>
>> Sure, but what's wrong with reading that file every 50 seconds? Almost
>> all boxes poll for media changes of optical drives and usb card
>> readers anyway, so it's not that we are not doing stuff like this
>> already.
>
> We poll for media because there's no event-based way of avoiding it - in
> this case there is.

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.

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?

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

Thanks,
Kay
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