Re: [Qemu-devel] [PATCH v4 4/9] target-ppc: improve lxvw4x implementation

[Nikunj A Dadhania]

David Gibson <address@hidden> writes:

> [ Unknown signature status ]
> On Wed, Sep 28, 2016 at 11:01:22AM +0530, Nikunj A Dadhania wrote:
>> Load 8byte at a time and manipulate.
>> 
>> Big-Endian Storage
>> +-------------+-------------+-------------+-------------+
>> | 00 11 22 33 | 44 55 66 77 | 88 99 AA BB | CC DD EE FF |
>> +-------------+-------------+-------------+-------------+
>> 
>> Little-Endian Storage
>> +-------------+-------------+-------------+-------------+
>> | 33 22 11 00 | 77 66 55 44 | BB AA 99 88 | FF EE DD CC |
>> +-------------+-------------+-------------+-------------+
>> 
>> Vector load results in:
>> +-------------+-------------+-------------+-------------+
>> | 00 11 22 33 | 44 55 66 77 | 88 99 AA BB | CC DD EE FF |
>> +-------------+-------------+-------------+-------------+
>
> Ok.  I'm guessing from this that implementing those GPR<->VSR
> instructions showed that the earlier versions were endian-incorrect as
> I suspected.
>
> Have you verified that this new implementation is actually faster (or
> at least no slower) on LE than the original implementation with
> individual 32-bit stores?

Result of million lxvw4x, mfvsrd/mfvsrld and print

Without patch:
==============
[tcg_test]$ time ../qemu/ppc64le-linux-user/qemu-ppc64le  -cpu POWER9 le_lxvw4x 
 >/dev/null
real    0m2.812s
user    0m2.792s
sys     0m0.020s
[tcg_test]$

With patch:
===========
[tcg_test]$ time ../qemu/ppc64le-linux-user/qemu-ppc64le  -cpu POWER9 le_lxvw4x 
 >/dev/null
real    0m2.801s
user    0m2.783s
sys     0m0.018s
[tcg_test]$

Not much perceivable difference, is there a better way to benchmark?

Regards
Nikunj