From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
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To: | Andres Freund <andres(at)anarazel(dot)de> |
Cc: | Ants Aasma <ants(dot)aasma(at)eesti(dot)ee>, Heikki Linnakangas <hlinnaka(at)iki(dot)fi>, Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: WIP: Faster Expression Processing v4 |
Date: | 2017-03-26 03:51:45 |
Message-ID: | 23529.1490500305@sss.pgh.pa.us |
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Andres Freund <andres(at)anarazel(dot)de> writes:
> On March 25, 2017 4:56:11 PM PDT, Ants Aasma <ants(dot)aasma(at)eesti(dot)ee> wrote:
>> I haven't had the time to research this properly, but initial tests
>> show that with GCC 6.2 adding
>>
>> #pragma GCC optimize ("no-crossjumping")
>>
>> fixes merging of the op tail jumps.
>>
>> Some quick and dirty benchmarking suggests that the benefit for the
>> interpreter is about 15% (5% speedup on a workload that spends 1/3 in
>> ExecInterpExpr). My idea of prefetching op->resnull/resvalue to local
>> vars before the indirect jump is somewhere between a tiny benefit and
>> no effect, certainly not worth introducing extra complexity. Clang 3.8
>> does the correct thing out of the box and is a couple of percent
>> faster than GCC with the pragma.
> That's large enough to be worth doing (although I recall you seeing all jumps commonalized). We should probably do this on a per function basis however (either using pragma push option, or function attributes).
Seems like it would be fine to do it on a per-file basis. If you're
worried about pessimizing the out-of-line subroutines, we could move
those to a different file --- it's pretty questionable that they're
in execExprInterp.c in the first place, considering they're meant to be
used by more than just that execution method.
regards, tom lane
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