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From: Jan Beulich <jbeulich@suse.com>
To: Hongyan Xia <hx242@xen.org>
Cc: Stefano Stabellini <sstabellini@kernel.org>,
	Julien Grall <julien@xen.org>, Wei Liu <wl@xen.org>,
	Andrew Cooper <andrew.cooper3@citrix.com>,
	Ian Jackson <ian.jackson@eu.citrix.com>,
	George Dunlap <george.dunlap@citrix.com>,
	xen-devel@lists.xenproject.org
Subject: Re: [Xen-devel] [PATCH] Revert "domctl: improve locking during domain destruction"
Date: Tue, 24 Mar 2020 17:13:45 +0100	[thread overview]
Message-ID: <37dcd2d8-8ffe-a58e-4c7a-6dafc935b1c1@suse.com> (raw)
In-Reply-To: <de46590ad566d9be55b26eaca0bc4dc7fbbada59.1585063311.git.hongyxia@amazon.com>

On 24.03.2020 16:21, Hongyan Xia wrote:
> From: Hongyan Xia <hongyxia@amazon.com>
> 
> Unfortunately, even though that commit dropped the domctl lock and
> allowed other domctl to continue, it created severe lock contention
> within domain destructions themselves. Multiple domain destructions in
> parallel now spin for the global heap lock when freeing memory and could
> spend a long time before the next hypercall continuation.

I'm not at all happy to see this reverted; instead I was hoping that
we could drop the domctl lock in further cases. If a lack of
continuations is the problem, did you try forcing them to occur more
frequently?

> 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.

Jan


  reply	other threads:[~2020-03-24 16:14 UTC|newest]

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-03-24 15:21 Hongyan Xia
2020-03-24 16:13 ` Jan Beulich [this message]
2020-03-24 18:39   ` Julien Grall
2020-03-25  7:11     ` Jan Beulich
2020-03-26 14:39       ` Hongyan Xia
2020-03-26 16:55       ` Jim Fehlig
2020-03-31 10:31         ` Julien Grall
2020-03-24 18:40 ` [Xen-devel] " Julien Grall

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