Re: More latency regressions with 2.6.11-rc4-RT-V0.7.39-02

Nick Piggin
2005-02-24T02:43:18Z

Lee Revell wrote:
> On Thu, 2005-02-24 at 12:29 +1100, Nick Piggin wrote:
>
>>Lee Revell wrote:
>>
>>>IIRC last time I really tested this a few months ago, the worst case
>>>latency on that machine was about 150us. Currently its 422us from the
>>>same clear_page_range code path.
>>>
>>
>>Well it should be pretty trivial to add a break in there.
>>I don't think it can get into 2.6.11 at this point though,
>>so we'll revisit this for 2.6.12 if the clear_page_range
>>optimisations don't get anywhere.
>>
>
>
> Agreed, it would be much better to optimize this away than just add a
> scheduling point. It seems like we could do this lazily.
>

Oh? What do you mean by lazy? IMO it is sort of implemented lazily now.
That is, we are too lazy to refcount page table pages in fastpaths, so
that pushes a lot of work to unmap time. Not necessarily a bad trade-off,
mind you. Just something I'm looking into.