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

["Roger Pau Monné" <roger.pau@citrix.com>]

On Tue, Nov 09, 2021 at 02:42:58PM +0000, Julien Grall wrote:
> Hi Roger,
> 
> On 09/11/2021 14:31, 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)
> 
> Thanks for the numbers, this is already an improvement from the reverted.
> 
> Can you also please provide some details on the setup that was used to get
> the number? (e.g. how many guests, amount of memory...).

Those are from Dmitry, and are gathered after destroying 5 guests in
parallel. Given his previous emails he seems to use 2GB HVM guests for
other tests, so I would assume that's the case for the lock profile data
also (albeit it's not said explicitly):

https://lists.xenproject.org/archives/html/xen-devel/2021-09/msg01515.html

I'm not sure it's worth adding this explicitly, as it's not a very
complex test case. Probably any attempts to destroy a minimal amount
of guests in parallel (5?) will already show the lock contention in
the profiling.

Thanks, Roger.