Re: [PATCH for-4.16 v2] Revert "domctl: improve locking during domain destruction"

[Julien Grall <julien@xxxxxxx>]

Hi Roger,

On 12/11/2021 12:02, Roger Pau Monne wrote:
> This reverts commit 228ab9992ffb1d8f9d2475f2581e68b2913acb88.
>
> Performance analysis has shown that dropping the domctl lock during
> domain destruction greatly increases the contention in the heap_lock,
> thus making parallel destruction of domains slower.
>
> The following lockperf data shows the difference between the current
> code and the reverted one:
>
> lock:  3342357(2.268295505s), block:  3263853(18.556650797s)
> lock:  2788704(0.362311723s), block:   222681( 0.091152276s)
>
> Those figures are from Dmitry Isaikin, and are gathered after
> destroying 5 2GB HVM guests in parallel:
>
> https://lists.xenproject.org/archives/html/xen-devel/2021-09/msg01515.html
>
> Given the current point in the release, revert the commit and
> reinstate holding the domctl lock during domain destruction. Further
> work should be done in order to re-add more fine grained locking to
> the domain destruction path once a proper solution to avoid the
> heap_lock contention is found.
>
> Reported-by: Hongyan Xia <hongyxia@xxxxxxxxxx>
> Reported-by: Dmitry Isaikin <isaikin-dmitry@xxxxxxxxx>
> Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
> Acked-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
Acked-by: Julien Grall <jgrall@xxxxxxxxxx>

Cheers,

--
Julien Grall