On Sun, Oct 14, 2018 at 04:17:31PM -0700, Paul E. McKenney wrote: > On Sun, Oct 14, 2018 at 02:29:55PM -0700, Joel Fernandes (Google) wrote: > > The Requirements.html document says "Disabling Preemption Does Not Block > > Grace Periods". However this is no longer true with the RCU > > consolidation. Lets remove the obsolete (non-)requirement entirely. > > > > Signed-off-by: Joel Fernandes (Google) <joel@xxxxxxxxxxxxxxxxx> > > Good catch, queued, thank you! Thanks! By the way after I sent the patch, I also tried Oleg's experiment to confirm that this is indeed obsolete. :) One thing interesting came up when I tried synchronize_rcu_expedited() instead of synchronize_rcu() in Oleg's experiment, I still saw a multiple millisecond delay between when the rcu read section completely and the synchronize_rcu_expedited returns: For example, with synchronize_rcu_expedited, the 'SPIN done' and the 'SYNC done' are about 3 millisecond apart: [ 77.599142] SPIN start [ 77.601595] SYNC start [ 82.604950] SPIN done! [ 82.607836] SYNC done! I saw anywhere from 2-6 milliseconds. The reason I bring this up is according to Requirements.html: In some cases, the multi-millisecond synchronize_rcu() latencies are unacceptable. In these cases, synchronize_rcu_expedited() may be used instead,.. so either I messed something up in the experiment, or I need to update this part of the document ;-) thanks, - Joel
