On Thu, Jun 12, 2014 at 06:35:15PM -0700, Paul E. McKenney wrote: > On Thu, Jun 12, 2014 at 06:24:32PM -0700, Paul E. McKenney wrote: > > On Fri, Jun 13, 2014 at 02:16:59AM +0200, Frederic Weisbecker wrote: > > > CONFIG_NO_HZ_FULL may be enabled widely on distros nowadays but actual > > > users should be a tiny minority, if actually any. > > > > > > Also there is a risk that affining the GP kthread to a single CPU could > > > end up noticeably reducing RCU performances and increasing energy > > > consumption. > > > > > > So lets affine the GP kthread only when nohz full is actually used > > > (ie: when the nohz_full= parameter is filled or CONFIG_NO_HZ_FULL_ALL=y) > > Which reminds me... Kernel-heavy workloads running NO_HZ_FULL_ALL=y > can see long RCU grace periods, as in about two seconds each. It is > not hard for me to detect this situation.
Ah yeah sounds quite long. > Is there some way I can > call for a given CPU's scheduling-clock interrupt to be turned on? Yeah, once the nohz kick patchset (https://lwn.net/Articles/601214/) is merged, a simple call to tick_nohz_full_kick_cpu() should do the trick. Although the right condition must be there on the IPI side. Maybe with rcu_needs_cpu() or such. But it would be interesting to identify the sources of these extended grace periods. If we only restart the tick, we may ignore some deeper oustanding issue. Thanks. > > I believe that the nsproxy guys were seeing something like this as well. > > Thanx, Paul -- 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/
