From mboxrd@z Thu Jan  1 00:00:00 1970
From: Julien Grall <julien.grall@linaro.org>
Subject: Re: xen/arm: VCPU scheduling
Date: Mon, 22 Dec 2014 11:36:58 +0100
Message-ID: <5497F44A.7030201@linaro.org>
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To: Vijay Kilari <vijay.kilari@gmail.com>, Ian Campbell <Ian.Campbell@citrix.com>, Stefano Stabellini <stefano.stabellini@eu.citrix.com>
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On 20/12/2014 20:48, Vijay Kilari wrote:
> Hi,

Hi Vijay,

>
>     I want to know what is the criteria followed in Xen for scheduling VCPUs.
> Assume below scenario:
>
>   - Run 2 VPCUs on 1 Physical CPU
>   - VCPUs does not trap on WFE or WFE ( either by WFI/WFE trap is
> disabled in HCR OR no WFE/WFI in EL1 is executed).
>
> In such scenario, does Xen assumes that VCPU0 is always running because it has
> NOT trapped on WFI and WFE (not yielded voluntary) and does not
> schedule VCPU1? or is it time shared?

The scheduler allocates time slice to each VCPU. Once the slice is 
ending, another VCPU may be scheduled.

Xen is also trapping WFE/WFI to allow better performance. Why would you 
want to disable WFE/WFI traps?

Regards,

-- 
Julien Grall