Hi Stefano,
On 21/02/17 17:49, Stefano Stabellini wrote:
On Tue, 21 Feb 2017, Dario Faggioli wrote:
On Tue, 2017-02-21 at 13:46 +0000, George Dunlap wrote:
Oh, actually, if --which I only now realize may be what you are
referring to, since you're talking about "guest burning its credits"--
you let the vCPU put the pCPU to sleep *but*, when it wakes up (or when
the scheduler runs again for whatever reason), you charge to it for all
the time the the pCPU was actually idle/sleeping, well, that may
actually not break scheduling, or cause disruption to the service of
other vCPUs.... But indeed I'd consider it rather counter intuitive a
behavior.
How can this be safe? There could be no interrupts programmed to wake up
the pcpu at all. In fact, I don't think today there would be any, unless
we set one up in Xen for the specific purpose of interrupting the pcpu
sleep.
I don't know the inner working of the scheduler, but does it always send
an interrupt to other pcpu to schedule something?
You still seem to assume that WFI/WFE is the only way to get a vCPU
unscheduled. If that was the case it would be utterly wrong because you
cannot expect a guest to use them.
What if there are 2 vcpu pinned to the same pcpu? This cannot be fair.
Why wouldn't it be fair? This is the same situation as a guest vCPU not
using WFI/WFE.
Cheers,
--
Julien Grall
_______________________________________________
Xen-devel mailing list
Xen-devel@lists.xen.org
https://lists.xen.org/xen-devel
