On Mon, 3 Apr 2006, Nathan Lynch wrote:
> > There are many other for_each_*_cpu loops in the kernel that do not have
> > any of the instrumentation you suggest. I suggest you come up with a
> > general solution and then go through all of them and fix this. Please be
> > aware that many of these loops are performance critical.
>
> But this one isn't, right?
Right. One could use more expensive processing here.
> And I'm afraid there's a misunderstanding here -- only
> for_each_online_cpu (or accessing the cpu online map in general) has
> such restrictions -- for_each_possible_cpu doesn't require any locking
> or preempt tricks since cpu_possible_map must not change after boot.
Correct. We may want to audit the kernel and check that each
for_each_possible_cpu or for_each_cpu is really correct. Developers
frequently assume that all processors are up. There may be some
complicated interactions with cpusets. Adding Paul to this.
However, note that I am not interested hotplug functionality. It is going
to be a difficult task to make the kernel shutdown processors correctly. I
can give you feedback but I am not going to do this work.
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