Re: Optmize bitmapword macros calc (src/backend/nodes/bitmapset.c)

Em seg., 29 de jan. de 2024 às 19:40, Nathan Bossart <
nathandbossart(at)gmail(dot)com> escreveu:

> On Tue, Jan 30, 2024 at 11:23:57AM +1300, David Rowley wrote:
> > On Tue, 30 Jan 2024 at 08:32, Nathan Bossart <nathandbossart(at)gmail(dot)com>
> wrote:
> >> I'm currently +0.1 for this change. I don't see any huge problem with
> >> trimming a few instructions, but I'm dubious there's any measurable
> impact.
> >> However, a cycle saved is a cycle earned...
> >
> > FWIW, In [1] and subsequent replies, there are several examples of
> > benchmarks where various bitmapset functions are sitting high in the
> > profiles. So I wouldn't be too surprised if such a small change to the
> > WORDNUM and BITNUM macros made a noticeable difference.
>
> Good to know, thanks. If there is indeed demonstrable improvement, I'd
> readily adjust my +0.1 to +1.
>
Following the suggestions, I did a quick test with one of the scripts.

Ubuntu 64 bits
gcc 12.3 64 bits

create table t1 (a int) partition by list(a);
select 'create table t1_'||x||' partition of t1 for values
in('||x||');' from generate_series(0,9)x;

test1.sql
select * from t1 where a > 1 and a < 3;

pgbench -U postgres -n -f test1.sql -T 15 postgres

head:

tps = 27983.182940
tps = 28916.903038
tps = 29051.878855

patched:

tps = 27517.301246
tps = 27848.684133
tps = 28669.367300

create table t2 (a int) partition by list(a);
select 'create table t2_'||x||' partition of t2 for values
in('||x||');' from generate_series(0,9999)x;

test2.sql
select * from t2 where a > 1 and a < 3;

pgbench -U postgres -n -f test2.sql -T 15 postgres

head:

tps = 27144.044463
tps = 28932.948620
tps = 29299.016248

patched:

tps = 27363.364039
tps = 28588.141586
tps = 28669.367300

To my complete surprise, the change is slower.
I can't say how, with fewer instructions, gcc makes the binary worse.

best regards,
Ranier Vilela