Re: [Xen-devel] [PATCH] xen:rtds:fix bug in accounting budget

[Meng Xu <xumengpanda@xxxxxxxxx>]

On Wed, Oct 19, 2016 at 11:13 AM, Meng Xu <mengxu@xxxxxxxxxxxxx> wrote:
> The bug is introduced in Xen 4.7 when we converted RTDS scheduler
> from quantum-driven model to event-driven model.
> We assumed rt_schedule() is always called for a VCPU
> before the VCPUs budget replenished handler.
> This assumption does not hold, when system is overloaded, or
> when the VCPU budget is almost equal its period.
>
> Buggy behavior:
> 1) A VCPU may get less budget that assigned in a period.
> 2) A full capacity VCPU, i.e., a VCPU whose period is equal to budget,
>    may not get any budget in some period.

I'm speculating that this bug may make a VCPU starve from receiving
budget. This may cause the dom0 to freeze for an arbitrary long time
in some "random" cases, especially if the dom0 only has one VCPU with
large period.

In the feature document, we said:
+# Known issues
+
+* OSSTest reports occasional failures on ARM.

Hopefully, this known issue can be fixed as well.

Meng

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