[Mesa-dev] Determinism in the results of llvmpipe?

[Andrew A.]

> Am 29.11.2016 um 15:18 schrieb Jose Fonseca:
>> Actually, IIUC https://github.com/divVerent/s2tc/wiki/libtxc_dxtn picks
>> colors at random, so its possible you have the same version of s2tc
>> library, but random colors are being picked.
>>
>> If so, you might to hack s2tc to not pick colors at random, or just
>> avoid S3TC textures if you can.
>>
>
> IIRC the "randomness" had no actual random bits in it, so as long as the
> same library is used on both machines the results should be the same.
> Albeit from the pictures it indeed looks like one has full decoding and
> the other not (it's not jist the obvious issues on the "D" but it's not
> quite smooth elsewhere neither).
>
> (Albeit I'm not quite sure if you have similar cpus, the  E3-1275 v3 is
> Haswell which has AVX2, the CPU E5-2673 v3 doesn't seem to exist or at
> least it's not in intel's database - if that's a v2 instead it would be
> Ivy Bridge lacking AVX2, just featuring AVX1. In this case you can still
> get slightly different results from texture sampling due to potentially
> different choice of AoS vs. SoA sampling, albeit nothing which would
> explain what you're seeing unless there's a bug somewhere...)
>
> Roland

The problem was indeed different versions of libtxc being used, so I
settled on using a consistent version of that library across the
systems, and now all is well.

I'm not sure why the 2673v3 is not in the arc, but whatever it is,
/proc/cpuinfo confirms it supports avx2.
The closest I could find in the ARC is:
http://ark.intel.com/products/81709/Intel-Xeon-Processor-E5-2670-v3-30M-Cache-2_30-GHz
Perhaps this 2673v3 was a stepping only shipped to customers like
MS/Amazon for use on Azure/AWS, but that's just a hunch. By the way,
is there an environment variable to lock mesa/llvmpipe to use AVX1 and
not AVX2?

Thanks for the help!