On 06/02/2015 14:46, Frederic Weisbecker wrote: > > When running a KVM guest on a system with NOHZ_FULL enabled > > I just need to clarify the motivation first, does the above situation > really happen? Ok some distros enable NOHZ_FULL to let the user stop > the tick in userspace. So most of the time, CONFIG_NOHZ_FULL=y but > nohz full is runtime disabled (we need to pass a nohz_full= boot > parameter to enable it). And when it is runtime disabled, there should > be no rcu nocb CPU. > > (Although not setting CPUs in nocb mode when nohz full is runtime disabled > is perhaps a recent change.) > > So for the problem to arise, one need to enable nohz_full and run KVM > guest. And I never heard about such workloads. Yeah, it's a new thing but Marcelo, Luiz and Rik have been having a lot of fun with them (with PREEMPT_RT too). They're getting pretty good results given the right tuning. I'll let Paul queue the patches for 3.21 then! Paolo > That said it's potentially > interesting to turn off the tick on the host when the guest runs. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
