5b5fc4e585
hardclock() tick should be run on every active CPU, or on only one. On my tests, avoiding extra interrupts because of this on 8-CPU Core i7 system with HZ=10000 saves about 2% of performance. At this moment option implemented only for global timers, as reprogramming per-CPU timers is too expensive now to be compensated by this benefit, especially since we still have to regularly run hardclock() on at least one active CPU to update system uptime. For global timer it is quite trivial: timer runs always, but we just skip IPIs to other CPUs when possible. Option is enabled by default now, keeping previous behavior, as periodic hardclock() calls are still used at least to implement setitimer(2) with ITIMER_VIRTUAL and ITIMER_PROF arguments. But since default schedulers don't depend on it since r232917, we are much more free to experiment with it. MFC after: 1 month |
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