On Sat, Jan 21, 2023 at 12:38:35AM +0000, Zhang, Qiang1 wrote: [...] > >If you are in an intermediate state, part way to a !nocb state — > >you may have missed a nocb-related accel and wake, correct? Why does that matter? > >Once we transition to a !nocb state, we do not do a post-qs-report accel+wake anyway > > Should it be transition to a !nocb state, we do a post-qs-report accel+wake. > > >as we clearly know from the discussion. So why do we need to do it if we missed it for > >the intermediate stage? So, I am not fully sure yet what that needac is doing and why it is needed. > > For de-offloading, when in the process of > de-offloading(rcu_segcblist_completely_offloaded() return false), we're not > doing bypass even though this rdp is offloaded > state(rcu_rdp_is_offloaded(rdp) return true), at this time, the rcuog > kthread probably won't accel+wakeup, so we do accel+wakeup in > rcu_report_qs_rdp(), as you say why does that matter? for !nocb state, > we've always tried to accel+wakeup as much as possible(compared to nocb), > let rcu callback be executed as soon as possible. > > This is just my personal opinion, please correct me if I am wrong. I think your opinion is correct. The acceleration after the QS reporting may be needed for the case where we are part way between the offload and de-offload state as in this state (which we could call limbo state), there does not seem to be anywhere that acceleration is performed, and if this state persists for a long period of time, then no other path can accelerate the CBs thus likely starving them as Frederic mentioned.. thanks, - Joel > Thanks > Zqiang > > > > > >Do not get me wrong, stellar work here. But I suggest challenge the assumptions and the design, not always just the code that was already written :), apologies for any misplaced or noisy advice. > > > >Thanks! > > > > - Joel > > > > > > Thanks > > Zqiang > > > >> > >> (I am out of office till Monday but will intermittently (maybe) check > >> in, RCU is one of those things that daydreaming tends to lend itself > >> to...) > >> > >> - Joel
