On Thu, Jun 02, 2022 at 02:06:50AM +0000, Zhang, Qiang1 wrote: > Hi All > > Currently, I have tested as follows: > > runqemu kvm slirp nographic qemuparams="-m 2048 -smp 4" > bootparams="isolcpus=2,3 nohz_full=2,3 rcu_nocbs=2,3 > rcutree.dump_tree=1, rcu_nocb_poll" -d > > rcu: Offload RCU callbacks from CPUs: 2-3. > rcu: Poll for callbacks from no-CBs CPUs. > rcu: rcu_organize_nocb_kthreads: No-CB GP kthread CPU 0: 1 (rcuog/0) > rcu: rcu_organize_nocb_kthreads: No-CB GP kthread CPU 2: 3 (rcuog/2) > > but I find the rt-fifo rcuog/0 kthreads always doing polling, but due > to the my_rdp->nocb_head_rdp always is empty, this doesn't do the > actual thing, Is it possible that we do not polling when the nocb_head_rdp linked list is empty, and polling when it is not empty. > > Any thought? >If I understand your question correctly, you would like to avoid polling when the rcuog kthread's CPU's rcu_data structure's nocb_head_rdp list is empty. This could happen only when all of the CPUs served by that rcuog kthread have been de-offloaded, correct? Yes, thanks Paul reply. I'll be more careful with my wording next time. > >If so, this is not currently a user-visible issue, but it would be good to fix it before offloading and de-offloading becomes user-visible. > >If this is what you were thinking, what did you have in mind for a fix? When rcu_nocb_poll is set and the rcuog kthread's CPU's rcu_data structure's nocb_head_rdp list is empty, treat rcuog kthread like non-polling mode and put them in the waitqueue(my_rdp->nocb_gp_wq) for waiting, when nocb_head_rdp list is not empty(rcu_nocb_poll && !list_empty(nocb_head_rdp)), re-entering periodic wake-up mode. I need yours opinion. Any thought? Thanks Zqiang > >(We need to get Frederic's view in any case, of course.) > > Thanx, Paul
