* Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxx> wrote: > * Ingo Molnar (mingo@xxxxxxx) wrote: > > > > * Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx> wrote: > > > > > Second cut of "big hammer" expedited RCU grace periods, but only > > > for rcu_bh. This creates another softirq vector, so that entering > > > this softirq vector will have forced an rcu_bh quiescent state (as > > > noted by Dave Miller). Use smp_call_function() to invoke > > > raise_softirq() on all CPUs in order to cause this to happen. > > > Track the CPUs that have passed through a quiescent state (or gone > > > offline) with a cpumask. > > > > hm, i'm still asking whether doing this would be simpler via a > > reschedule vector - which not only is an existing facility but also > > forces all RCU domains through a quiescent state - not just bh-RCU > > participants. > > > > Triggering a new softirq is in no way simpler that doing an SMP > > cross-call - in fact softirqs are a finite resource so using some > > other facility would be preferred. > > > > Am i missing something? > > > > I think the reason for this whole thread is that waiting for rcu > quiescent state, when called many times e.g. in multiple iptables > invokations, takes too longs (5 seconds to load the netfilter > rules at boot). [...] I'm aware of the problem space. I was suggesting that to trigger the quiescent state and to wait for it to propagate it would be enough to reuse the reschedule mechanism. It would be relatively straightforward: first a send-reschedule then do a wait_task_context_switch() on rq->curr - both are existing primitives. (a task reference has to be taken but that's pretty much all) By the time wait_task_context_switch() returns from the last CPU we know that the quiescent state has passed. Ingo -- To unsubscribe from this list: send the line "unsubscribe netfilter-devel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
