2017-04-11 2:01 GMT+08:00 Frederic Weisbecker <[email protected]>: > On Mon, Apr 10, 2017 at 05:45:56PM +0200, Thomas Gleixner wrote: >> On Wed, 5 Apr 2017, Wanpeng Li wrote: >> > + /* >> > + * Offset the tick to avert jiffies_lock contention, and all ticks >> > + * alignment in order that the vtime sampling does not end up "in >> > + * phase" with the jiffies incrementing. >> > + */ >> > + if (sched_skew_tick || tick_nohz_full_enabled()) { >> > u64 offset = ktime_to_ns(tick_period) >> 1; >> > do_div(offset, num_possible_cpus()); >> > offset *= smp_processor_id(); >> >> That's not a fix, that's just papering over the problem. >> >> offset = 1ms / 2 = 500us = 500000ns; >> offset /= 144 = 3472ns >> >> So CPU0 and CPU1 ticks are ~3 microseconds apart. That merily reduces the >> probability of the issue, but does not prevent it. > > I worried about it but didn't realize it could be that tight. > > So the alternative is the solution involving sched_clock() as the source for > cputime. Wanpeng Li could you please resubmit your patch that does that?
Yeah, I will try it. Regards, Wanpeng Li
