* Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote: > > > Ingo Molnar <mingo@xxxxxxx> wrote: > > > > I have this fix queued up currently: > > > > 09223371deac: rcu: Use softirq to address performance regression > > I really don't think that is even close to enough. Yeah. > It still does all the callbacks in the threads, and according to > Peter, about half the rcu time in the threads remained.. You are right - things that are a few percent on a 24 core machine will definitely go exponentially worse on larger boxen. We'll get rid of the kthreads entirely. The funny thing about this workload is that context-switches are really a fastpath here and we are using anonymous IRQ-triggered softirqs embedded in random task contexts as a workaround for that. [ I think we'll have to revisit this issue and do it properly: quiescent state is mostly defined by context-switches here, so we could do the RCU callbacks from the task that turns a CPU quiescent, right in the scheduler context-switch path - perhaps with an option for SCHED_FIFO tasks to *not* do GC. That could possibly be more cache-efficient than softirq execution, as we'll process a still-hot pool of callbacks instead of doing them only once per timer tick. It will also make the RCU GC behavior HZ independent. ] In any case the proxy kthread model clearly sucked, no argument about that. Thanks, Ingo -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>