Messages in this thread | | | Date | Sat, 9 Jan 2010 16:03:18 -0800 | From | "Paul E. McKenney" <> | Subject | Re: [RFC PATCH] introduce sys_membarrier(): process-wide memory barrier |
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On Sat, Jan 09, 2010 at 06:16:40PM -0500, Steven Rostedt wrote: > On Sat, 2010-01-09 at 18:05 -0500, Steven Rostedt wrote: > > > Then we should have O(tasks) for spinlocks taken, and > > O(min(tasks, CPUS)) for IPIs. > > And for nr tasks >> CPUS, this may help too: > > > cpumask = 0; > > foreach task { > > if (cpumask == online_cpus) > break; > > > spin_lock(task_rq(task)->rq->lock); > > if (task_rq(task)->curr == task) > > cpu_set(task_cpu(task), cpumask); > > spin_unlock(task_rq(task)->rq->lock); > > } > > send_ipi(cpumask);
Good point, erring on the side of sending too many IPIs is safe. One might even be able to just send the full set if enough of the CPUs were running the current process and none of the remainder were running real-time threads. And yes, it would then be necessary to throttle calls to sys_membarrier().
Quickly hiding behind a suitable boulder... ;-)
Thanx, Paul
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