RE: [tip:tracing/hw-branch-tracing] tracing/hw-branch-tracing:convert bts-tracer mutex to a spinlock

[Metzger, Markus T]

>-----Original Message-----
>From: Ingo Molnar [mailto:mingo@xxxxxxx]
>Sent: Wednesday, February 25, 2009 12:11 PM
>To: Metzger, Markus T
>Cc: hpa@xxxxxxxxx; mingo@xxxxxxxxxx; tglx@xxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; linux-tip-
>commits@xxxxxxxxxxxxxxx


>> And I assume you like the spinlock better than the
>> get/put_online_cpus(), as well.
>
>yeah - and get/put_online_cpus is sleepable too, so it doesnt
>really help unless i'm missing something ...

I suggested to use get/put_online_cpus() instead of the lock.

The hotplug code waits until the cpu_hotplug.refcount is zero
and it holds the cpu_hotplug.lock during hotplug operations
(see cpu_hotplug_begin/done()).

In turn, get_online_cpus() needs to grab the cpu_hotplug.lock
to increment the cpu_hotplug.refcount.

Thus, we will use the cpu_hotplug.lock instead of our own lock.

regards,
markus.

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