Messages in this thread | | | Date | Fri, 11 Jan 2002 01:48:36 +0100 (CET) | From | Ingo Molnar <> | Subject | Re: [patch] O(1) scheduler, -G1, 2.5.2-pre10, 2.4.17 (fwd) |
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On Thu, 10 Jan 2002, Mike Kravetz wrote:
> If I run 3 cpu-hog tasks on a 2 CPU system, then 1 task will get an > entire CPU while the other 2 tasks share the other CPU (easily > verified by a simple test program). On previous versions of the > scheduler 'balancing' this load was achieved by the global nature of > time slices. No task was given a new time slice until the time slices > of all runnable tasks had expired. In the current scheduler, the > decision to replenish time slices is made at a local (pre-CPU) level. > I assume the load balancing code should take care of the above > workload? OR is this the behavior we desire? [...]
Arguably this is the most extreme situation - every other distribution (2:3, 3:4) is much less problematic. Will this cause problems? We could make the fairness-balancer more 'sharp' so that it will oscillate the length of the two runqueues at a slow pace, but it's still caching loss.
> We certainly have optimal cache use.
indeed. The question is, should we migrate processes around just to get 100% fairness in 'top' output? The (implicit) cost of a task migration (caused by the destruction & rebuilding of cache state) can be 10 milliseconds easily on a system with big caches.
Ingo
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