Messages in this thread | | | Date | Sun, 8 Oct 2023 00:04:00 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCH 00/15] sched: EEVDF and latency-nice and/or slice-attr |
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On Thu, Oct 05, 2023 at 02:05:57PM +0200, Peter Zijlstra wrote:
> t=10 V=4 t=10 V=4 > A |----< A |----< > B |< >B |< > >C |----------------< C |----------------< > |---*-----|---------|---------|---------|---- |---*-----|---------|---------|---------|---- >
> > t=52 V=18 t=36 V=13 > A |----< A |----< > >B |< B |< > C |----------------< >C |----------------< > |---------|-------*-|---------|---------|---- |---------|--*------|---------|---------|---- >
> > BAaaBCccccccccBBBAaaBBBAaaBB BBAaaBBBAaaBBBAaaBCccccccccB > > > > As I wrote before; EVDF has worse lag bounds, but this is not > insurmountable. The biggest problem that I can see is that of wakeup > preemption. Currently we allow to preempt when 'current' has reached V > (RUN_TO_PARITY in pick_eevdf()). > > With these rules, when EEVDF schedules C (our large slice task) at t=10 > above, it is only a little behind C and can be reaily preempted after > about 2 time units. > > However, EVDF will delay scheduling C until much later, see how A and B > walk far ahead of V until t=36. Only when will we pick C. But this means > that we're firmly stuck with C for at least 11 time units. A newly > placed task will be around V and will have no chance to preempt.
Playing around with it a little:
EEVDF EVDF
slice 30000000 slice 30000000 # Min Latencies: 00014 # Min Latencies: 00048 # Avg Latencies: 00692 # Avg Latencies: 188239 # Max Latencies: 94633 # Max Latencies: 961241 slice 3000000 slice 3000000 # Min Latencies: 00054 # Min Latencies: 00055 # Avg Latencies: 00522 # Avg Latencies: 00673 # Max Latencies: 41475 # Max Latencies: 13297 slice 300000 slice 300000 # Min Latencies: 00018 # Min Latencies: 00024 # Avg Latencies: 00344 # Avg Latencies: 00056 # Max Latencies: 20061 # Max Latencies: 00860
So while it improves the short slices, it completely blows up the large slices -- utterly slaughters the large slices in fact.
And all the many variants of BIAS_ELIGIBLE that I've tried so far only manage to murder the high end while simultaneously not actually helping the low end -- so that's a complete write off.
By far the sanest option so far is PLACE_SLEEPER -- and that is very much not a nice option either :-(
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