Re: Marginal performance improvement for fast-path locking

On Thu, Nov 28, 2013 at 2:23 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> Robert Haas <robertmhaas(at)gmail(dot)com> writes:
>> On Thu, Nov 28, 2013 at 1:46 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>>> We could add an extra test in FastPathGrantRelationLock's loop to make
>>> it remember the first unused slot rather than the last one, but that
>>> would add some cycles there, partially negating any benefit. Instead
>>> I propose that we reverse the direction of the search loop, as attached.
>
>> Well, the reason why the array is only 64 bytes in size is to make
>> sure that searching the whole thing is really fast. We figure we're
>> going to have to do that often, so it needs to be cheap. If it's not,
>> we're hosed already, I think.
>
> I actually suspect the bitmask manipulations cost more than the touches
> of fpRelId[]. I agree that there's no reason to think that this area
> needs really tense micro-optimization, but if we can get some savings for
> zero added cost/complexity, why not?

Sure.

--
Robert Haas
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