Messages in this thread |  | | | Date | Sat, 9 Jan 2010 20:12:55 -0500 | | From | Mathieu Desnoyers <> | | Subject | Re: [RFC PATCH] introduce sys_membarrier(): process-wide memory barrier |
| |
* Paul E. McKenney (paulmck@linux.vnet.ibm.com) wrote: > 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... ;-)
:)
One quick counter-argument against IPI-to-all: that will wake up all CPUs, including those which are asleep. Not really good for energy-saving.
Mathieu
> > Thanx, Paul
-- Mathieu Desnoyers OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68
|  |