On Wed, Nov 30, 2016 at 05:38:20PM +0100, Peter Zijlstra wrote: > On Wed, Nov 30, 2016 at 06:29:55AM -0800, Paul E. McKenney wrote: > > We can, and you are correct that cond_resched() does not unconditionally > > supply RCU quiescent states, and never has. Last time I tried to add > > cond_resched_rcu_qs() semantics to cond_resched(), I got told "no", > > but perhaps it is time to try again. > > Well, you got told: "ARRGH my benchmark goes all regress", or something > along those lines. Didn't we recently dig out those commits for some > reason or other? Were "those commits" the benchmark or putting cond_resched_rcu_qs() functionality into cond_resched()? Either way, no idea. > Finding out what benchmark that was and running it against this patch > would make sense. Agreed, especially given that I believe cond_resched_rcu_qs() is lighter weight than it used to be. No idea what benchmarks they were, though. > Also, I seem to have missed, why are we going through this again? People are running workloads that force long-running loops in the kernel, which get them RCU CPU stall warning messages. My reaction has been to insert cond_resched_rcu_qs() as needed, and Michal wondered why cond_resched() couldn't just handle both scheduling latency and RCU quiescent states. I remembered trying it, but not what the issue was. So I posted the patch assuming that I would eventually either find out what the issue was or that the issue no longer applied. ;-) Thanx, Paul -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>