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


  • To: Julien Grall <julien@xxxxxxx>
  • From: Roger Pau Monné <roger.pau@xxxxxxxxxx>
  • Date: Tue, 9 Nov 2021 15:55:50 +0100
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  • Cc: <xen-devel@xxxxxxxxxxxxxxxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, George Dunlap <george.dunlap@xxxxxxxxxx>, Jan Beulich <jbeulich@xxxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, Hongyan Xia <hongyxia@xxxxxxxxxx>, Dmitry Isaikin <isaikin-dmitry@xxxxxxxxx>, Ian Jackson <iwj@xxxxxxxxxxxxxx>
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  • List-id: Xen developer discussion <xen-devel.lists.xenproject.org>

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.



 


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