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SubjectRe: [PATCH 02/11] Add "handle page fault" PV helper.
On 11/08/2009 04:51 AM, Ingo Molnar wrote:
>
> * Avi Kivity <avi@redhat.com> wrote:
>
>> On 11/08/2009 01:36 PM, Ingo Molnar wrote:
>>>> Three existing callbacks are: kmemcheck, mmiotrace, notifier. Two
>>>> of them kmemcheck, mmiotrace are enabled only for debugging, should
>>>> not be performance concern. And notifier call sites (two of them)
>>>> are deliberately, as explained by comment, not at the function entry,
>>>> so can't be unified with others. (And kmemcheck also has two different
>>>> call site BTW)
>>>
>>> We want mmiotrace to be generic distro capable so the overhead when
>>> the hook is not used is of concern.
>>
>> Maybe we should generalize paravirt-ops patching in case if (x) f() is
>> deemed too expensive.
>
> Yes, that's a nice idea. We have quite a number of 'conditional
> callbacks' in various critical paths that could be made lighter via such
> a technique.
>
> It would also free new callbacks from the 'it increases overhead even if
> unused' criticism and made it easier to add them.
>

There are a number of other things were we permanently bind to a single
instance of something, too. Optimizing those away would be nice.
Consider memcpy(), where we may want to have different implementations
for different processors.

-hpa


--
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel. I don't speak on their behalf.



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