Messages in this thread | | | Date | Fri, 26 May 2006 23:59:15 +1000 | From | Peter Williams <> | Subject | Re: [RFC 3/5] sched: Add CPU rate hard caps |
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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.
> These two in > combination have shown resistance to any priority inversion problems in > widespread testing. An attempt was made to track semaphores held via a > down_interruptible() but unfortunately the lack of strict rules about who > could release the semaphore meant accounting was impossible of this scenario. > In practice, though there were no test cases that showed it to be an issue, > and the recent conversion en-masse of semaphores to mutexes in the kernel > means it has pretty much covered most possibilities. >
Thanks, Peter -- Peter Williams pwil3058@bigpond.net.au
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