On Wed, Dec 18, 2013 at 10:04:43AM +0800, Alex Shi wrote: > On 12/18/2013 06:51 AM, Frederic Weisbecker wrote: > > So this is what this series brings, more details following: > > > > * Some code, naming and whitespace cleanups > > > > * Allow all CPUs outside the nohz_full range to handle the timekeeping > > duty, not just CPU 0. Balancing the timekeeping duty should improve > > powersavings. > > If the system just has one nohz_full cpu running, it will need another > cpu to do timerkeeper job. Then the system roughly needs 2 cpu living. > From powersaving POV, that is not good compare to normal nohz idle.
Sure, but everything has a tradeoff :) We could theoretically run with the timekeeper purely idle if the other CPU in full dynticks mode runs in userspace for a long while and seldom do syscalls and faults. Timekeeping could be updated on kernel/user boundaries in this case without much impact on performances. But then there is one strict condition for that: it can't read the timeofday through the vdso but only through a syscall. Then if we can meet that condition, then CPU 0 could as well be full dynticks. Now that's real extreme HPC ;) -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
