Hello, Frederic, On Tue, 1 Apr 2025 16:27:36 GMT, Frederic Weisbecker wrote: > Le Mon, Mar 31, 2025 at 02:29:52PM -0700, Paul E. McKenney a écrit : > > The disagreement is a feature, at least up to a point. That feature > > allows CPUs to go idle for long periods without RCU having to bother > > them or to mess with their per-CPU data (give or take ->gpwrap). It also > > allows per-rcu_node-leaf locking, which is important on large systems. > > > > Trying to make precisely globally agreed-on beginnings and ends of > > RCU grace periods will not end well from performance, scalability, > > or real-time-response viewpoints. ;-) > > The distributed disagreement is definetly a feature. The duplicate root > is more debatable. > > > But simplifications that don't hurt performance, scalability, and > > real-time-response are of course welcome. > > I'm not even sure my proposal is a simplification. Perhaps it is. Another > hope is that it could avoid future accidents. >
Aside from the performance concerns: Sorry if this is silly but could you provide a small hint as to how unifying the global counter with the node affects QS reporting or hotplug? It was not immediately obvious to me. Thanks for the help. Thanks! - Joel > > Indeed, this probably needs actual performance results showing that > > it is needed. My guess is that only systems with a single rcu_node > > structure that is both leaf and root would have any chance of noticing. > > And those tend to have few CPUs, so they might not care. > > Do you have any idea for a benchmark to test here? > > Thanks. > > > Thanx, Paul
