Re: [Xen-devel] [PATCH v2] x86/time: update vtsc_last with cmpxchg and drop vtsc_lock

[Jan Beulich <jbeulich@xxxxxxxx>]

On 19.12.2019 17:03, Igor Druzhinin wrote:
> Now that vtsc_last is the only entity protected by vtsc_lock we can
> simply update it using a single atomic operation and drop the spinlock
> entirely. This is extremely important for the case of running nested
> (e.g. shim instance with lots of vCPUs assigned) since if preemption
> happens somewhere inside the critical section that would immediately
> mean that other vCPU stop progressing (and probably being preempted
> as well) waiting for the spinlock to be freed.
> 
> This fixes constant shim guest boot lockups with ~32 vCPUs if there is
> vCPU overcommit present (which increases the likelihood of preemption).
> 
> Signed-off-by: Igor Druzhinin <igor.druzhinin@xxxxxxxxxx>

Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>

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