Re: [RFC 3/5] sched: Add CPU rate hard caps

[Con Kolivas <kernel@kolivas.org>]

On Friday 26 May 2006 23:59, Peter Williams wrote:
> Con Kolivas wrote:
> > On Friday 26 May 2006 14:20, Peter Williams wrote:
> >> This patch implements hard CPU rate caps per task as a proportion of a
> >> single CPU's capacity expressed in parts per thousand.
> >
> > A hard cap of 1/1000 could lead to interesting starvation scenarios where
> > a mutex or semaphore was held by a task that hardly ever got cpu. Same
> > goes to a lesser extent to a 0 soft cap.
> >
> > Here is how I handle idleprio tasks in current -ck:
> >
> > http://ck.kolivas.org/patches/2.6/pre-releases/2.6.17-rc5/2.6.17-rc5-ck1/
> >patches/track_mutexes-1.patch tags tasks that are holding a mutex
> >
> > http://ck.kolivas.org/patches/2.6/pre-releases/2.6.17-rc5/2.6.17-rc5-ck1/
> >patches/sched-idleprio-1.7.patch is the idleprio policy for staircase.
> >
> > What it does is runs idleprio tasks as normal tasks when they hold a
> > mutex or are waking up after calling down() (ie holding a semaphore).
>
> I wasn't aware that you could detect those conditions.  They could be
> very useful.

Ingo's mutex infrastructure made it possible to accurately track mutexes held, 
and basically anything entering uninterruptible sleep has called down(). 
Mainline, as you know, already flags the latter for interactivity purposes.

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