svn commit: r313006 - in head: sys/conf sys/libkern sys/libkern/x86 sys/sys tests/sys/kern

[Conrad Meyer]

On Wed, Mar 1, 2017 at 9:27 PM, Bruce Evans <brde at optusnet.com.au> wrote:
> On Wed, 1 Mar 2017, Conrad Meyer wrote:
>
>> On my laptop (Intel(R) Core(TM) i5-3320M CPU — Ivy Bridge) I still see
>> a little worse performance with this patch.  Please excuse the ugly
>> graphs, I don't have a better graphing tool set up at this time:
>>
>> https://people.freebsd.org/~cem/crc32/sse42_bde.png
>> https://people.freebsd.org/~cem/crc32/sse42_bde_log.png
>
>
> Try doubling the loop sizes.  There shouldn't be any significant difference
> above size 3*LONG unless LONG is too small.  Apparently it is too small for
> older CPUs.
>
> I now have a Sandybridge i5-2xxx laptop to test on, but don't have it set
> up for much yet.
>
> Bruce


Hi Bruce,

Doubling the loop sizes seems to make it slightly worse, actually:

https://people.freebsd.org/~cem/crc32/sse42_bde2.png
https://people.freebsd.org/~cem/crc32/sse42_bde_log2.png

I haven't made any attempt to inspect the generated assembly.  This is
Clang 3.9.1 with -O2.

Best,
Conrad