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

Kay Sievers
2009-11-19T13:31:21Z

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)?

Kay