Messages in this thread | | | Date | Sun, 18 May 2003 10:55:17 +0200 | From | Mike Galbraith <> | Subject | RE: Scheduling problem with 2.4? |
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At 05:16 PM 5/17/2003 -0700, David Schwartz wrote:
> > I see what you mean, but I still don't think it is a problem. If > > bandwidth matters you will have to use large writes and reads anyways, > > if bandwidth doesn't matter the number of ctx switches doesn't matter > > either and latency usually is way more important with small messages. > > > Andrea > > This is the danger of pre-emption based upon dynamic priorities. > You can >get cases where two processes each are permitted to make a very small amount >of progress in alternation. This can happen just as well with large writes >as small ones, the amount of data is irrelevent, it's the amount of CPU time >that's important, or to put it another way, it's how far a process can get >without suffering a context switch. > > I suggest that a process be permitted to use up at least some > portion of >its timeslice exempt from any pre-emption based solely on dynamic >priorities.
Cool.
Thank you for the spiffy idea. I implemented this in my (hack/chop) mm5 tree in about 30 seconds, and it works just fine. Very simple time_after(jiffies, p->last_run + MIN_TIMESLICE) checks in wake_up_cpu() plus the obvious dinky change to schedule(), and it worked instantly. Hmm.. I wonder if this might help some of the other scheduler (seemingly) bad behavior as well.
Is there any down-side to not preempting quite as often? It seems like there should be a bandwidth gain.
-Mike
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