Re: [Xen-devel] [PATCH v4] xen/arm: introduce vwfi parameter

[Julien Grall <julien.grall@xxxxxxx>]

Hi Stefano,

On 01/03/17 19:43, Stefano Stabellini wrote:
> Introduce new Xen command line parameter called "vwfi", which stands for
> virtual wfi. The default is "trap": Xen traps guest wfi and wfe
> instructions. In the case of wfi, Xen calls vcpu_block on the guest
> vcpu; in the case of guest wfe, Xen calls vcpu_yield on the guest vcpu.
> The behavior can be changed by setting vwfi to "native", in that case
> Xen doesn't trap neither wfi nor wfe, running them in guest context.
>
> The result is strong reduction in irq latency (from 5000ns to 2000ns,
> measured using https://github.com/edgarigl/tbm, the physical timer, and
> 1 pcpu dedicated to 1 vcpu). The downside is that the scheduler thinks
> that the guest is busy when actually is sleeping, leading to suboptimal
> scheduling decisions.
>
> Signed-off-by: Stefano Stabellini <sstabellini@xxxxxxxxxx>
Reviewed-by: Julien Grall <julien.grall@xxxxxxx>

Cheers,

--
Julien Grall

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