Re: PostgreSQLv14 TPC-H performance GCC vs Clang

> GCC vs Clang

related:
As I see - with LLVM/Clang 14.0 ( X86_64 -O3 ) ~12% performance increase
expected with the new optimisation ( probably adapted from gcc )
- https://twitter.com/djtodoro/status/1466808507240386560
-
https://www.phoronix.com/scan.php?page=news_item&px=LLVM-Clang-14-Hoist-Load

regards,
Imre

arjun shetty <arjunshetty955(at)gmail(dot)com> ezt írta (időpont: 2021. nov. 16.,
K, 11:10):

> Yes, currently focusing affects queries as well.
> In meanwhile on analysis(hardware level) and sample examples noticed
> 1. GCC performance better than Clang on int128 .
> 2. Clang performance better than GCC on long long
> the reference example
> https://stackoverflow.com/questions/63029428/why-is-int128-t-faster-than-long-long-on-x86-64-gcc
>
> 3.GCC enabled with “ fexcess-precision=standard” (precision cast for
> floating point ).
>
> Is these 3 points can make performance difference GCC vs Clang in
> PostgreSQLv14 in Apple/AMD/()environment(intel environment need to check).
> In these environment int128 enabled wrt PostgreSQLv14.
>
> On Friday, November 5, 2021, Tomas Vondra <tomas(dot)vondra(at)enterprisedb(dot)com>
> wrote:
>
>> Hi,
>>
>> IMO this thread provides so little information it's almost impossible to
>> answer the question. There's almost no information about the hardware,
>> scale of the test, configuration of the Postgres instance, the exact build
>> flags, differences in generated asm code, etc.
>>
>> I find it hard to believe merely switching from clang to gcc yields 22%
>> speedup - that's way higher than any differences we've seen in the past.
>>
>> In my experience, the speedup is unlikely to be "across the board". There
>> will be a handful of affected queries, while most remaining queries will be
>> about the same. In that case you need to focus on those queries, see if the
>> plans are the same, do some profiling, etc.
>>
>>
>> regards
>>
>> --
>> Tomas Vondra
>> EnterpriseDB: http://www.enterprisedb.com
>> The Enterprise PostgreSQL Company
>>
>