On Mon, Dec 13, 2021 at 11:32:56AM -0800, Paul E. McKenney wrote: > On Mon, Dec 13, 2021 at 08:09:22AM +0000, Woodhouse, David wrote: > > On Mon, 2021-12-13 at 12:30 +0530, Neeraj Upadhyay wrote: > > > To support onlining multiple CPUs concurrently, > > > change rcu_state.n_online_cpus updates to be atomic. > > > Note, it's ok for rcu_blocking_is_gp() to do a > > > atomic_read(&rcu_state.n_online_cpus), as the > > > value of .n_online_cpus switches from 1->2, in > > > rcutree_prepare_cpu(), which runs before the new > > > CPU comes online. Similarly 2->1 transition happens > > > from rcutree_dead_cpu(), which executes after the > > > CPU is offlined, and runs on the last online CPU. > > > > > > Signed-off-by: Neeraj Upadhyay <quic_neeraju@xxxxxxxxxxx> > > > > In my parallel-bringup series, the prepare stages are still being > > executed in series on the BSP, so I don't think this patch is needed > > yet. I'm not sure we'd ever end up with the prepare stages being done > > in parallel — the most I see us doing is onlining a single *batch* of > > CPUs at a time, much like bringup_nonboot_cpus() does. > > > > But this patch certainly doesn't *hurt*. > > > > Acked-by: David Woodhouse <dwmw@xxxxxxxxxxxx> > > Queued for further review and testing. > > To Frederic's point, this won't go to mainline unless it is actually > needed, but it will at least be pulled into a branch in -rcu marked with > a tag for future reference. Ok, sounds reasonable then. Thanks!
