On Fri, Mar 31, 2017 at 04:09:10PM -0400, Luiz Capitulino wrote: > On Thu, 30 Mar 2017 17:25:46 -0400 > Luiz Capitulino <lcapitul...@redhat.com> wrote: > > > On Thu, 30 Mar 2017 16:18:17 +0200 > > Frederic Weisbecker <fweis...@gmail.com> wrote: > > > > > On Thu, Mar 30, 2017 at 09:59:54PM +0800, Wanpeng Li wrote: > > > > 2017-03-30 21:38 GMT+08:00 Frederic Weisbecker <fweis...@gmail.com>: > > > > > If it works, we may want to take that solution, likely less > > > > > performance sensitive > > > > > than using sched_clock(). In fact sched_clock() is fast, especially > > > > > as we require it to > > > > > be stable for nohz_full, but using it involves costly conversion back > > > > > and forth to jiffies. > > > > > > > > So both Rik and you agree with the skew tick solution, I will try it > > > > tomorrow. Btw, if we should just add random offset to the cpu in the > > > > nohz_full mode or add random offset to all cpus like the codes above? > > > > > > > > > > Lets just keep it to all CPUs for simplicty. > > > Also please add a comment that explains why we need that skew_tick on > > > nohz_full. > > > > I've tried all the test-cases we discussed in this thread with skew_tick=1 > > and it worked as expected in bare-metal and KVM guests. > > > > However, I found a test-case that works in bare-metal but show problems > > in KVM guests. It could something that's KVM specific, or it could be > > something that's harder to reproduce in bare-metal. > > After discussing some findings on this issue with Rik, I realized that > we don't add the skew when restarting the tick in tick_nohz_restart(). > Adding the offset there seems to solve this problem.
Are you sure? tick_nohz_restart() doesn't seem to override the initial skew. It always forwards the expiration time on top of the last tick.
