Re: [Xen-devel] [PATCH] Avoid endless loop for vcpu migration

[Keir Fraser <keir.xen@xxxxxxxxx>]

On 15/03/2011 09:21, "Juergen Gross" <juergen.gross@xxxxxxxxxxxxxx> wrote:

>> That candidate-is-valid check seems absolutely independent of the
>> particular scheduler used, and hence could be done in the (sole)
>> caller, thus not requiring any change to the scheduler interface.
>> 
>> Which at once would eliminate unnecessary calls into pick_cpu (i.e.
>> you'd call it a second time only if the previously selected CPU really
>> is no longer valid to be used for that vCPU).
> 
> True.
> 
> The patch seems to become smaller :-)

By the way, why is the cpu_isset(new_cpu, v->domain->vcpupool->cpu_valid)
check required (after calling pick_cpu, in the cuirrently checked-in code)?
You already check that pick_cpu was called holding the correct pair of
locks, if it has returned a cpu that is not in the pool's cpu_valid mask,
what would make pick_cpu return anything different on the next invocation
thus avoiding an endless loop?

Looks like this question would remain even if this new patch was applied.

 -- Keir



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