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 ;-) -- 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
