Re: [Xen-devel] [PATCH 1/2] smp: convert the cpu maps lock into a rw lock

[Julien Grall <julien@xxxxxxx>]

Hi Roger,

On 13/02/2020 11:32, Roger Pau Monne wrote:
> Most users of the cpu maps just care about the maps not changing while
> the lock is being held, but don't actually modify the maps.
>
> Convert the lock into a rw lock, and take the lock in read mode in
> get_cpu_maps and in write mode in cpu_hotplug_begin. This will lower
> the contention around the lock, since plug and unplug operations that
> take the lock in write mode are not that common.
>
> Note that the read lock can be taken recursively (as it's a shared
> lock), and hence will keep the same behavior as the previously used
> recursive lock. As for the write lock, it's only used by CPU
> plug/unplug operations, and the lock is never taken recursively in
> that case.
>
> While there also change get_cpu_maps return type to bool.
>
> Reported-by: Julien Grall <julien@xxxxxxx>
> Suggested-also-by: Jan Beulich <jbeulich@xxxxxxxx>
> Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
Reviewed-by: Julien Grall <julien@xxxxxxx>

Cheers,

--
Julien Grall

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxxx
https://lists.xenproject.org/mailman/listinfo/xen-devel