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

Matthew Garrett
2009-11-19T14:16:46Z

On Thu, Nov 19, 2009 at 02:29:29PM +0100, Kay Sievers wrote:
> On Thu, Nov 19, 2009 at 14:01, Matthew Garrett <mjg@redhat.com> wrote:
> > On Thu, Nov 19, 2009 at 12:09:30PM +0100, Kay Sievers wrote:
> >> On Wed, Nov 18, 2009 at 22:33, Matthew Garrett <mjg59@srcf.ucam.org> wrote:
> >> > My use cases are on the order of a second.
> >>
> >> Ok, what's the specific use case, which should be triggered after a
> >> second? I thought you were thinking about disk spindown or similar.
> >
> > The first is altering ALPM policy. ALPM will be initiated by the host if
> > the number of queued requests hits zero - if there's no hysteresis
> > implemented, then that can result in a significant performance hit. We
> > don't need /much/ hysteresis, but it's the difference between a 50%
> > performance hit and not having that.
>
> Can't that logic live entirely in the kernel, instead of being a
> rather generic userspace event interface (with the current limitation
> to a single user)?

It could, but it seems a bit of a hack. It'd still also require the
timer to be in the kernel, so we might as well expose that to userspace.

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