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Re: [Xen-devel] [PATCH] schedule: mask out XEN_RUNSTATE_UPDATE from state entry time
- To: Andrii Anisov <andrii.anisov@xxxxxxxxx>
- From: Jan Beulich <JBeulich@xxxxxxxx>
- Date: Thu, 18 Jul 2019 11:10:08 +0000
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- Cc: George Dunlap <george.dunlap@xxxxxxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>, Andrii Anisov <andrii_anisov@xxxxxxxx>, Dario Faggioli <dfaggioli@xxxxxxxx>
- Delivery-date: Thu, 18 Jul 2019 11:10:42 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
- Thread-index: AQHVPU7dWxB3gAbicEW8M/sijNABxqbQOA+A
- Thread-topic: [Xen-devel] [PATCH] schedule: mask out XEN_RUNSTATE_UPDATE from state entry time
On 18.07.2019 11:54, Andrii Anisov wrote:
> Using XEN_RUNSTATE_UPDATE mask during the process of copying runstate
> values to guest causes runstate entry time to be eventually considered
> negative on a calculation of the time delta. So the XEN_RUNSTATE_UPDATE
> should be masked out during the calculation of the time spent in the
> particular runstate.
A concrete scenario where update_runstate_area() and vcpu_runstate_change()
can actually race would be very worthwhile to point out here. In particular
on Arm I'm not (yet?) seeing how this could happen.
Considering the value of XEN_RUNSTATE_UPDATE it must be a rather rare race
anyway, I would guess.
Jan
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