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Re: [Xen-devel] [PATCH] Revert "domctl: improve locking during domain destruction"

On 24/03/2020 16:13, Jan Beulich wrote:
On 24.03.2020 16:21, Hongyan Xia wrote:
From: Hongyan Xia <hongyxia@xxxxxxxxxx>
In contrast,
after dropping that commit, parallel domain destructions will just fail
to take the domctl lock, creating a hypercall continuation and backing
off immediately, allowing the thread that holds the lock to destroy a
domain much more quickly and allowing backed-off threads to process
events and irqs.

On a 144-core server with 4TiB of memory, destroying 32 guests (each
with 4 vcpus and 122GiB memory) simultaneously takes:

before the revert: 29 minutes
after the revert: 6 minutes

This wants comparing against numbers demonstrating the bad effects of
the global domctl lock. Iirc they were quite a bit higher than 6 min,
perhaps depending on guest properties.

Your original commit message doesn't contain any clue in which cases the domctl lock was an issue. So please provide information on the setups you think it will make it worse.


Julien Grall



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