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

[Mike Galbraith <efault@gmx.de>]

On Fri, 2006-05-26 at 23:59 +1000, 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.

Isn't this exactly what the PI code is there to handle?  Is something
more than PI needed?

	-Mike