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

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 04.03.14 at 12:52, Andrew Cooper <andrew.cooper3@xxxxxxxxxx> wrote:
> 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.

I agree, but I wanted to do one step at a time. Judging how much
work we want to permit done between preemption points will be
either heavy guess work, or require quite a bit of performance
measurement...

Jan


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