Messages in this thread | | | Date | Thu, 18 Nov 2010 16:32:29 +0100 | From | Oleg Nesterov <> | Subject | Re: [PATCH] sched: Simplify cpu-hot-unplug task migration |
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On 11/18, Peter Zijlstra wrote: > > There is no firm guarantee the dying cpu actually got to running the > idle thread (there's a guarantee it will at some point), so we ought to > maintain that wait-loop, possibly using cpu_relax(), I don't see the > point in calling yield() here.
Agreed. But do we need to wait at all?
With or without this change, even if we know that rq->idle is running we can't know if it (say) already started play_dead_common() or not.
We are going to call __cpu_die(), afaics it should do the necessary synchronization in any case.
For example, native_cpu_die() waits for cpu_state == CPU_DEAD in a loop. Of course it should work in practice (it also does msleep), but in theory there is no guarantee.
So. Can't we just remove this wait-loop? We know that rq->idle will be scheduled "soon", I don't understand why it is necessary to ensure that context_switch() has already happened.
Oleg.
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