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

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Message-Id: <1154222579.2467.12.camel@entropy>
Date:	Sat, 29 Jul 2006 18:22:59 -0700
From:	Nicholas Miell <nmiell@...cast.net>
To:	Bill Huey <billh@...ppy.monkey.org>
Cc:	Edgar Toernig <froese@....de>, Neil Horman <nhorman@...driver.com>,
	Jim Gettys <jg@...top.org>, "H. Peter Anvin" <hpa@...or.com>,
	Dave Airlie <airlied@...il.com>,
	Segher Boessenkool <segher@...nel.crashing.org>,
	linux-kernel@...r.kernel.org, a.zummo@...ertech.it,
	jg@...edesktop.org, Keith Packard <keithp@...thp.com>,
	Ingo Molnar <mingo@...e.hu>,
	Steven Rostedt <rostedt@...dmis.org>
Subject: Re: itimer again (Re: [PATCH] RTC: Add mmap method to rtc
	character driver)

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@...cast.net>

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