Re: [PATCH] [RFC] Add support for uevents on block device idle

[Matthew Garrett <mjg59@srcf.ucam.org>]

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