Re: [Xen-devel] [PATCH 0/2] make hypercall preemption checks consistent

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 04/03/14 11:21, Jan Beulich wrote:
> - never preempt on the first iteration (ensure forward progress)
> - never preempt on the last iteration (pointless/wasteful)
> - do cheap checks first
>
> 1: common: make hypercall preemption checks consistent
> 2: x86: make hypercall preemption checks consistent
>
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

All in all, this is a good improvement over what is currently present.

However, given the overhead of creating continuations (particularly for
32bit HVM guests, which have been seen to unconditionally fail the
preemption check by the time the compat layer has run), some of these
operations would probably be better having more than a single guaranteed
operation.

~Andrew

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