[Tarantool-patches] [PATCH v6 4/5] datetime: perf test for datetime parser

Safin Timur tsafin at tarantool.org
Thu Aug 19 13:29:06 MSK 2021

On 19.08.2021 13:19, Serge Petrenko wrote:
> 19.08.2021 05:56, Timur Safin пишет:
>> It was told that if field `datetime.secs` would be `double` we should get
>> better performance in LuaJIT instead of `uint64_t` type, which is used 
>> at the
>> moment.
>> So we have created benchmark, which was comparing implementations of 
>> functions
>> from `datetime.c` if we would use `double` or `int64_t` for 
>> `datetime.secs` field.
>> Despite expectations, based on prior experience with floaing-point on x86
>> processors, comparison shows that `double` provides similar or
>> sometimes better timings. And picture stays consistent be it SSE2, 
>> AVX1 or
>> AVX2 code.
>> Part of #5941
>> ---
> I agree with Vladimir here.
> Looks like this perf test doesn't belong to Tarantool repository.
> Would you mind dropping it?

Here is the case (we both aware of) I want to avoid here - today we do 
not have saved _that_ decimal perf test, basing on which we have 
preferred LuaC and dropped FFI implementation. We could not rerun it 
today, within a newer LuaJIT implementation, to verify that situation 
didn't change. This is similar case - we have made a decision basing on 
some evaluations using this code, in a future we may decide to further 
optimize data structure (like Vova suggested elsewhere to split int64 
into 2 fields), and it would be better if at that moment we would still 
have performance test around for adaptations and rerun.

Yes, it's another test of performance test we used to see in perf 
directory (hehe, there is only single test at the moment), kind of one 
time shot in a history, important for design decision, but from longer 
prospective I assume it should be still around.

Does my reasoning make some sense?


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