Thread: pgsql: Use Intel SSE 4.2 CRC instructions where available.

Use Intel SSE 4.2 CRC instructions where available.

Modern x86 and x86-64 processors with SSE 4.2 support have special
instructions, crc32b and crc32q, for calculating CRC-32C. They greatly
speed up CRC calculation.

Whether the instructions can be used or not depends on the compiler and the
target architecture. If generation of SSE 4.2 instructions is allowed for
the target (-msse4.2 flag on gcc and clang), use them. If they are not
allowed by default, but the compiler supports the -msse4.2 flag to enable
them, compile just the CRC-32C function with -msse4.2 flag, and check at
runtime whether the processor we're running on supports it. If it doesn't,
fall back to the slicing-by-8 algorithm. (With the common defaults on
current operating systems, the runtime-check variant is what you get in
practice.)

Abhijit Menon-Sen, heavily modified by me, reviewed by Andres Freund.

Branch
------
master

Details
-------
http://git.postgresql.org/pg/commitdiff/3dc2d62d0486325bf263655c2d9a96aee0b02abe

Modified Files
--------------
config/c-compiler.m4          |   27 ++++++
configure                     |  212 +++++++++++++++++++++++++++++++++++++++++
configure.in                  |   78 +++++++++++++++
src/Makefile.global.in        |    4 +
src/include/pg_config.h.in    |   15 +++
src/include/pg_config.h.win32 |   23 ++++-
src/include/port/pg_crc32c.h  |   44 +++++++++
src/port/Makefile             |    8 +-
src/port/pg_crc32c_choose.c   |   63 ++++++++++++
src/port/pg_crc32c_sse42.c    |   52 ++++++++++
src/tools/msvc/Mkvcbuild.pm   |   13 ++-
11 files changed, 534 insertions(+), 5 deletions(-)

On 14 April 2015 at 10:09, Heikki Linnakangas <heikki.linnakangas@iki.fi> wrote:

> Abhijit Menon-Sen, heavily modified by me, reviewed by Andres Freund.

Did the heavy modifications have any affect on the patch behaviour, or
was this just related to where you would like to put the code?

I know you like to rewrite things your way, just wanted to check what
happened. Thanks.

--
 Simon Riggs                   http://www.2ndQuadrant.com/
 PostgreSQL Development, 24x7 Support, RemoteDBA, Training & Services

Heikki Linnakangas <heikki.linnakangas@iki.fi> writes:
> Whether the instructions can be used or not depends on the compiler and the
> target architecture. If generation of SSE 4.2 instructions is allowed for
> the target (-msse4.2 flag on gcc and clang), use them. If they are not
> allowed by default, but the compiler supports the -msse4.2 flag to enable
> them, compile just the CRC-32C function with -msse4.2 flag, and check at
> runtime whether the processor we're running on supports it. If it doesn't,
> fall back to the slicing-by-8 algorithm. (With the common defaults on
> current operating systems, the runtime-check variant is what you get in
> practice.)

The buildfarm says this doesn't work terribly well, at least not with icc.

            regards, tom lane