[llvm-dev] Can I control HSA config generated by AMDGPU backend?

[UE US via llvm-dev]

On Wed, Sep 5, 2018 at 1:17 PM Changdao Dong via llvm-dev <
llvm-dev at lists.llvm.org> wrote:

>
> Finally I kind of modified llvm to generate assembly that can run on
> AMDGPU pro drivers. One problem is the performance of the code generated by
> llvm is about 10% slower than amdgpu's online compiler. Anything I can tune
> the performance up the performance of llvm?\
>
> Thanks!
>
> On Tue, Sep 4, 2018 at 9:23 AM 董昌道 <dongchangdao at gmail.com> wrote:
>
>> I am writing a miner of crypto currency, for which most users run it with
>> amdgpu driver. I have written a script the translate the meta data of LLVM
>> isa format into clrxasm format.
>>
>
clrxasm's docs say it only supports GCN devices to begin with, so it seems
like you wouldn't actually want to use the --amdhsa "os" flag (or the
amdgpu target, you'd want amdgcn);  that's for things that will be directly
loaded with the HSA API as far as I know.  If you felt like it you could
load and execute them with that API instead of the opencl one and not mess
around with it further than that.  I've never worked with that, so Artem
can probably tell you more if that doesn't explain things.  It looks
relatively straightforward.
https://gpuopen.com/rocm-with-harmony-combining-opencl-hcc-hsa-in-a-single-program/

This page  https://openwall.info/wiki/john/development/AMD-IL (linked from
another AMD list posting last year about something similar)   says that the
following work:

*(i)*Setting the environment variable:
AMD_OCL_BUILD_OPTIONS_APPEND=-save-temps ./Name_of_executable
*(ii)*Using the build options:
In clBuildProram() specify ”-save-temps” in the build option field to
generate IL and ISA.

...and the driver will retain the .isa and .il files, but then you'd still
be left with patching in your changes somehow.   If that works it would at
least give you an example of what LLVM is currently generating vs. the
driver so you can compare those and also modify / test assembly changes to
determine if they're worthwhile for whatever issue you're trying to solve.

If this is an optimization thing, I'd strongly suggest going through the
files as-is and trying to perform some of the ocl-level optimizations AMD's
guides suggest.  You'd be surprised what removing a couple of conditionals
in often-called loops can do for performance of many things.    Looking at
the code, vectorizing / using native opencl data types would probably show
some gains as well.  Many of them seem to be straight C source conversions
of stuff that was optimized for x86 at some point before SSE2 existed and
promptly  forgotten.

Cheers,
-G
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20180906/102c2b32/attachment.html>