Messages in this thread | | | Date | Sat, 06 Sep 2003 16:38:05 +1000 | From | Nick Piggin <> | Subject | Re: [PATCH] Nick's scheduler policy v12 |
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Martin J. Bligh wrote:
>>Yep, as Mike mentioned, renicing X causes it to get bigger >>timeslices with the stock scheduler. If you had 2 nice -20 processes, >>they would each get a timeslice of 200ms, so you're harming their >>latency. >> > >Well, if I can be naive for a second (and I'll fully admit I don't >understand the implications of this), there are two things here - >either give it more of a timeslice (bandwidth increase), or make it >more interactive (latency increase). Those two seem to be separable, >but we don't bother. Seems better to pass a more subtle hint to the >scheduler that this is interactive - nice seems like a very large >brick between the eyes. >
I think the two will always related. One means giving a higher dynamic priority, the other a bigger timeslice. So you want say gcc to have a 100ms timeslice with lowest scheduling prio, but X to have a 20ms slice and a very high scheduling priority.
Unfortunately, the way the scheduler currently works, X might use all its timeslice, then have to wait 100ms for gcc to finish its. The way I do it is give a small timeslice to high prio tasks, and lower priority tasks get progressively less.
When _only_ low priority tasks are running, they'll all get long timeslices.
> >>>There may be some more details around this, and I'd love to hear them, >>>but I fundmantally believe that explitit fiddling with particular >>>processes because we believe they're somehow magic is wrong (and so >>>does Linus, from previous discussions). >>> >>Well it would be nice if someone could find out how to do it, but I >>think that if we want X to be able to get 80% CPU when 2 other CPU hogs >>are running, you have to renice it. >> > >OK. So you renice it ... then your two cpu jobs exit, and you kick off >xmms. Every time you waggle a window, X will steal the cpu back from >xmms, and it'll stall, surely? That's what seemed to happen before. >I don't see how you can fix anything by doing static priority alterations >(eg nice), because the workload changes. > >I'm probably missing something ... feel free to slap me ;-) >
OK well just as a rough idea of how mine works: worst case for xmms is that X is at its highest dynamic priority (and reniced). xmms will be at its highest dynamic prio, or maybe one or two below that.
X will get to run for maybe 30ms first, then xmms is allowed 6ms. That is still 15% CPU. And X soon comes down in priority if it continues to use a lot of CPU.
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