Re: JIT compiling with LLVM v12.2

On March 30, 2018 10:04:25 AM PDT, Konstantin Knizhnik  wrote:
>
>
>On 30.03.2018 18:54, Andres Freund wrote:
>> On 2018-03-30 15:12:05 +0300, Konstantin Knizhnik wrote:
>>> I have repeated performance tests at my computer and find out some
>>> regression comparing with previous JIT version.
>>> Previously JIT provides about 2 times improvement at TPC-H Q1. Now
>the
>>> difference is reduced to 1.4 without parallel execution and 1.3 with
>>> parallel execution:
>> Huh. That's the same computer you did the tests on?
>>
>> There shouldn't have been any, I'll check it out.
>>
>> - Andres
>
>Yes, it is the same computer.
>But sorry, may be it is false alarm.
>I noticed that the time of normal (non-jit) query execution was also 
>faster in the past: for parallel execution 6549 vs. 7550 now, for 
>non-parallel execution 20075 vs. 25100.
>I do not know whether this difference is caused by some changes in 
>Postgres committed since this time (end of January) or just because of 
>different layout of data in memory.

A brief attempt at bisecting would be good. That's quite the regression. Possibly it's OS related though. Meltdown / Spectre?

Andres
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