[Bf-committers] Cycles CUDA Toolkit 8 transition

PerfectionCat sindra1961reborn at yahoo.co.jp
Wed Aug 3 00:27:55 CEST 2016


blender which built using a source file at the time of 467e12514e60 in CUDA8 has a shorter time required for rendering of BMW for around 20 seconds.

SHA-1-2f5db2e45b7a8af51b15c45bb41f5dcb49ae9d4d is slow.
SHA-1-467e12514e60b4130cd0a33b59f53aa4cf7056b6 is fast.

Windows 10 pro 64bits

Intel i7 6700K 4.4GHz

With best regards, PerfectionCat.

----- Original Message -----
>From: Sergey Sharybin <sergey.vfx at gmail.com>
>To: Blender Developers <bf-committers at blender.org> 
>Date: 2016/8/2, Tue 23:44
>Subject: Re: [Bf-committers] Cycles CUDA Toolkit 8 transition
>Hey again,
>Spent majority of the day trying to solve the regression, without much
>success. Even simplest kernel needed for BMW scene is about 10% slower.
>This is mainly coming from bump nodes. Enabling all other features makes
>things even worse performance wise.
>I did some tweaks again to make sure all functions are inlined in the same
>manner by CUDA 8.0 as they used to be before. So now PTax output shows
>exactly same function, but for some reason spills are just higher with new
>toolkit and at the same time stack usage is reasonably slower. Not sure yet
>what's going on here and think we'd better leave this alone for until
>official toolkit is released.
>For the time being i've switched buildbots to use more complicated setup,
>using CUDA 7.5 for all kernels except sm_60 and sm_61 (new generation
>cards) and using new toolkit only for new kernels.
>So hopefully now all maxwell and lower crads have same performance as
>before. And yet users of new cards can have some degree of GPU rendering.
>On Mon, Aug 1, 2016 at 6:15 PM, Sergey Sharybin <sergey.vfx at gmail.com>
>> Hey everyone,
>> In order to make Cycles officially support new Pascal cards (GTX 10x0) it
>> is crucial to use CUDA Toolkit 8. While it is still in the RC stage we
>> started looking into making it official one for Cycles.
>> There is already some initial work done:
>> - Tweaks are done to Cycles kernel to have same level of inlined functions
>> (new toolkit barely used inlined functions, which resulted in poor
>> performance on all cards)
>> - New toolkit was installed onto all release environments and buildbots.
>> So on a positive side, next buildbot's builds will support Pascal cards,
>> yay! :)
>> But unfortunately, while i've managed to keep Kepler cards (GTX760) same
>> performance as before, we had a report from Jens in IRC about Maxwell cards
>> having a poor performance yet again (in his case, up to 40% worse).
>> This is really unacceptable, we'll keep working on solution for this
>> issue. It might take some time, so just be aware and please be patient :)
>> I will keep posted here with our progress.
>> --
>> With best regards, Sergey Sharybin
>With best regards, Sergey Sharybin
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>Bf-committers at blender.org

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