On 11/29/2011 02:05 AM, Benjamin Herrenschmidt wrote: > On Mon, 2011-11-28 at 16:32 +0530, Deepthi Dharwar wrote: > >>> Additionally, I'm a bit worried (but maybe we already discussed that a >>> while back, I don't know) but cpu_idle_wait() has "wait" in the name, >>> which makes me think it might need to actually -wait- for all cpus to >>> have come out of the function. >> >> cpu_idle_wait is used to ensure that all the CPUs discard old idle >> handler and update to new one. Required while changing idle >> handler on SMP systems. >> >>> Now your implementation doesn't provide that guarantee. It might be >>> fine, I don't know, but if it is, you'd better document it well in the >>> comments surrounding the code, because as it is, all you do is shoot an >>> interrupt which will cause the target CPU to eventually come out of idle >>> some time in the future. >> >> >> I was hoping that sending an explicit reschedule to the cpus would >> do the trick but sure we can add some documentation around the code. > > Well, the question is what guarantee do you expect. Sending a reschedule > IPI will take the other CPUs out of the actual sleep mode, but it will > be some time from there back to getting out of the handler function > (first back out of hypervisor etc...). > > The code as you implemented it doesn't wait for that to happen. It might > be fine ... or not. I don't know what semantics you are after precisely. > > Cheers, > Ben. > > Yes, this could be problematic as there is small window for the race condition to occur . Otherwise we need to manually schedule it by running a kernel thread but this would definitely have a overhead and would be an overkill. Regards, Deepthi _______________________________________________ linux-pm mailing list linux-pm@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/linux-pm
