Bug#843425: Fwd: Bug#843425: blender doesn't optimize for amd64 defaults

[Sergey Sharybin]

Hi again, and sorry for too much noise..

I've checked the compiler output of i386 build of blender from [1] and
there's such status print:

-- SSE and SSE2 optimizations are DISABLED!

Meaning, there's no SSE/SSE2 global optimization of i386 builds of
Blender in Debian already (thanks to Matteo i guess :)

Is there anything else here to be solved?

[1] https://buildd.debian.org/status/package.php?p=blender

On Mon, Nov 7, 2016 at 10:52 AM, Sergey Sharybin <sergey at blender.org> wrote:
> Ah, it's Pemtium 4 where SSE2 first arrived, for a moment thought it's
> Pentium Pro. My bad..
>
> So for both i386 and i686 SSE2 requirement is not valid.
>
> Currently in Blender upstream we detect SSE/SSE2 flags based on
> current CPU. Meaning, if you're builing on i686 CPU Blender should
> already have global SSE2 optimization disabled. If CPU on the builder
> machine supports SSE2 we can still force SSE/SSE2 optimization to be
> off by passing `-DSUPPORT_SSE_BUILD=OFF -DSUPPORT_SSE2_BUILD=OFF` to
> CMake.
>
> On Mon, Nov 7, 2016 at 10:40 AM, Matthias Klose <doko at debian.org> wrote:
>> On 07.11.2016 10:32, Sergey Sharybin wrote:
>>> Hi,
>>>
>>> Afraid the reply to #843425 was only delivered to the BTS and not easily
>>> visible to you guys.
>>>
>>> Here's the full reply, same as [1]. Just so you know :)
>>>
>>> [1] https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=843425#10
>>>
>>>
>>> ---------- Forwarded message ----------
>>> From: Sergey Sharybin <sergey at blender.org>
>>> Date: Mon, Nov 7, 2016 at 9:50 AM
>>> Subject: Bug#843425: blender doesn't optimize for amd64 defaults
>>> To: 843425 at bugs.debian.org
>>>
>>>
>>> Hi,
>>>
>>> From the report it's not fully clear what parts Blender those CFLAGS
>>> are referencing to, but because it's all within a context of #843379 i
>>> would guess we are talking about Cycles kernel here (Cycles is the
>>> render engine we use in Blender).
>>>
>>> In this case you're partially correct: we are mainly ignoring default
>>> CFLAGS but we compile 6 different CPU kernels, optimized for various
>>> microarchitectures ("native" - no SSE2 on i686 / SSE2 on amd64, forced
>>> SSE2, SSE3, SSE4.1, AVX and AVX2). Then during runtime we detect
>>> current CPU microarchitecture and invoke kernel with highest
>>> capabilities allowed on the current processor.
>>>
>>> This is the only way we can guarantee optimal render times on amd64.
>>> Keep in mind, AVX2 can render similar scene like 2x faster than simple
>>> SSE2. This is something we can not ignore for our users.
>>
>> well, the GCC issue was opened with a RC severity, so I assumed that everything
>> was built using these flags. The assumption of amd64 having SSE2 enabled by
>> defaults is valid.
>>
>>> That being said, if you have some tricky setup where we do not detect
>>> capabilities correctly and Cycles tries to use unsupported kernel and
>>> runs into ILLEGAL INSTRUCTION i'll be happy to look into and solve
>>> that from our end.
>>>
>>> Now, about forcing microarchitecture in rest of Blender. We do require
>>> SSE2 on amd64 and i686, but that should be all fine as far as i know
>>> (amd64 always have SSE2, 32bit builds will disable SSE2 automatically
>>> if current CPU does not support it).
>>
>> For Debian it is not ok to assume SSE2 on the i386 architecture.
>>
>> Matthias
>>
>
> --
> With best regards, Sergey Sharybin



-- 
With best regards, Sergey Sharybin