On Wed, 2007-10-31 at 22:53 +0100, Andi Kleen wrote: > Peter Zijlstra <[email protected]> writes: > > > Use HR-timers (when available) to deliver an accurate preemption tick. > > > > The regular scheduler tick that runs at 1/HZ can be too coarse when nice > > level are used. The fairness system will still keep the cpu utilisation 'fair' > > by then delaying the task that got an excessive amount of CPU time but try to > > minimize this by delivering preemption points spot-on. > > This might be costly when hrtimers happen to use an more expensive > to reprogram time source. Even an APIC timer access is fairly slow. > And you'll potentially add the to lots of context switces. > > Not sure that is a good idea for performance in general. Right, now I remember. The idea was to run the rest of the kernel at HZ=50 or so, nothing but scheduling needs it anymore, and with this patch the scheduler doesn't need it anymore either. Should be good for power. This new hrtick thing only does a lot of ticks when there are a lot of runnable tasks, it starts at 2 with a tick per latency/2.
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