Re: itimer again (Re: [PATCH] RTC: Add mmap method to rtc character driver)

Nicholas Miell
2006-07-30T01:23:09Z

On Sat, 2006-07-29 at 18:00 -0700, Bill Huey wrote:
> On Sat, Jul 29, 2006 at 04:35:51PM -0700, Nicholas Miell wrote:
> > On Sat, 2006-07-29 at 15:51 -0700, Bill Huey wrote:
> > > [CCing Steve and Ingo on this thread]
> > >
> > > It's a different topic than what Keith needs, but this is useful for another
> > > set of purposes. It's something that's really useful in the RT patch since
> > > there isn't a decent API to get at high resolution timers in userspace. What
> > > you've written is something that I articulated to Steve Rostedt over a dinner
> > > at OLS and is badly needed in the -rt patches IMO. I suggest targeting that
> > > for some kind of inclusion to Ingo Molnar's patchset.
> > >
> >
> > Do you mind summarizing what's wrong with the existing interfaces for
> > those of us who didn't have the opportunity to join you for dinner at
> > OLS?
>
> Think edge triggered verse level triggered. Event interfaces in the Linux
> kernel are sort of just that, edge triggered events. What RT folks generally
> want is control over scheduling policies over a particular time period in
> relation to a scheduling policy. A general kernel event interface isn't
^ Did you mean to say timer here?
> going to cut it for those purpose and wasn't design to deal with those cases
> in the first place.

So you're asking for an automatic (perhaps temporary) change in
scheduling policy when a particular timer expires (or perhaps on
occurrence of other types of events)?

I think Windows automatically boosts the priority of a thread when it
delivers an I/O completion notification, and I'm pretty sure that
Microsoft has a patent related to that.

--
Nicholas Miell <nmiell@comcast.net>