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. > 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
