Re: [PATCH 3/3] x86, extable: Handle early exceptions

H. Peter Anvin
2012-04-19T20:21:20Z

On 04/19/2012 01:17 PM, David Daney wrote:
> On 04/19/2012 11:55 AM, H. Peter Anvin wrote:
>> Either way I suggest picking up David's presorting patchset since it
>> is already done and use its infrastructure for any further improvements.
>
> It does have the advantage of already being implemented. There was a
> little feedback on the kbuild portions of the patch.
>
> If you would like, I will send an updated version of the patch.

Please. It gets us 90% of the way, and we need the infrastructure
anyway to do any further work.

>> As far as a linear probe you get an average of n lookups with a
>> packing density of 1-1/n so you are right; a linear probe with a
>> density of say 1/2 is probably best.
>>
>
> I usually see exception table sizes on the order of 2^10 entries, so I
> have to wonder how much you really gain from an O(1) implementation.

Well, for either variant of hash table you end up with ~2 serial memory
references as opposed to ~11. No idea if there are workloads where this
actually matters.

-hpa