| From: | Robert Haas <robertmhaas(at)gmail(dot)com> |
|---|---|
| To: | Konstantin Knizhnik <k(dot)knizhnik(at)postgrespro(dot)ru> |
| Cc: | Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com>, Merlin Moncure <mmoncure(at)gmail(dot)com>, PostgreSQL Hackers <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: Why JIT speed improvement is so modest? |
| Date: | 2019-12-06 15:53:44 |
| Message-ID: | CA+TgmoYewAaYNQFALyTCTaBuGW0uay0+wHkEGaQAwaPK1PkZ1Q@mail.gmail.com |
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On Thu, Nov 28, 2019 at 2:08 AM Konstantin Knizhnik
<k(dot)knizhnik(at)postgrespro(dot)ru> wrote:
> calls float4_accum for each row of T, the same query in VOPS will call
> vops_float4_avg_accumulate for each tile which contains 64 elements.
> So vops_float4_avg_accumulate is called 64 times less than float4_accum.
> And inside it contains straightforward loop:
>
> for (i = 0; i < TILE_SIZE; i++) {
> sum += opd->payload[i];
> }
>
> which can be optimized by compiler (loop unrolling, use of SIMD
> instructions,...).
Part of the reason why the compiler can optimize that so well is
probably related to the fact that it includes no overflow checks.
--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company
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