On Thu, Dec 15, 2016 at 09:07:14AM -0500, Steven Rostedt wrote: > On Thu, 15 Dec 2016 14:47:37 +0100 > Daniel Bristot de Oliveira <daniel@xxxxxxxxxx> wrote: > > > Hi Chris, > > > > On 12/12/2016 11:42 PM, Chris Friesen wrote: > > > Based on the fact that Documentation/kernel-per-CPU-kthreads.txt > > > describes CONFIG_RCU_NOCB_CPU_ALL=y as a solution by preventing the > > > rcuc/%u kthreads from having any work to do, I had expected that the > > > "rcu_nocbs=1-15" kernel parameter would have a similar effect. > > Paul, would rcu_nocbs=1-15 work? Or should ALL be used ? I'm assuming > this is on a 16 CPUs box, in which case I don't see much of a difference > for not just using ALL as it is almost there anyway ;-) Using ALL is equivalent to rcu_nocbs=0-15 (as opposed to rcu_nocbs=1-15) on a 16-CPU box, assuming that the CPUs are numbered consecutively. The only case where I could see a difference is if you were running something like Rik's nasty Java workload on CPU 0, in which case rcu_nocbs=1-15 would be the better choice. Thanx, Paul > -- Steve > > > > > As far as I recall, using CONFIG_RCU_NOCB_CPU_ALL=y will prevent the RCU > > callbacks from running on rcuc/X threads (which are pinned to the CPU > > X), but the rcuc/X thread is still in charge of awaking the ruco* > > threads of the CPU X. > > > > > Does anyone have any idea what's going on here, and how I can prevent > > > the rcuc/<cpu> tasks from waking up? > > > > You can try to use rcu_nocb_poll kernel parameter to unload the rcuc/X > > thread of the task of awaking its respective ruco*s threads. > > > > >From [1]: > > > > rcu_nocb_poll [KNL] > > Rather than requiring that offloaded CPUs > > (specified by rcu_nocbs= above) explicitly > > awaken the corresponding "rcuoN" kthreads, > > make these kthreads poll for callbacks. > > This improves the real-time response for the > > offloaded CPUs by relieving them of the need to > > wake up the corresponding kthread, but degrades > > energy efficiency by requiring that the kthreads > > periodically wake up to do the polling. > > > > [1] https://www.kernel.org/doc/Documentation/kernel-parameters.txt > > > > -- Daniel > > -- > > To unsubscribe from this list: send the line "unsubscribe linux-rt-users" in > > the body of a message to majordomo@xxxxxxxxxxxxxxx > > More majordomo info at http://vger.kernel.org/majordomo-info.html > -- To unsubscribe from this list: send the line "unsubscribe linux-rt-users" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
