[LLVMdev] Supporting heterogeneous computing in llvm.

[Gerolf Hoflehner]

Hi Christos,

your idea can certainly go very far, and the capability of extracting and executing one loop nest at a time should enable progress in multiple directions, among them fast performance evaluation of loop transformations and benefits of accelerators. It could also be useful for measuring and tuning off-loading overhead.

Cheers
Gerolf
> On Jun 5, 2015, at 3:01 AM, Christos Margiolas <chrmargiolas at gmail.com> wrote:
> 
> Hi Gerolf, 
> 
> LLVM already has a Utility class for extracting loops to functions. However extracting code to a different module is something that is missing I think. Supporting a homogeneous variant is something I have considered and in fact the debug plugin I have written is a homogeneous variant. I "offload" to the same architecture. The idea could be further extended in a scheme where the offloaded code is loaded in a third process and the main process performs remote process calls. This would probably require extensive data transfers across the address spaces or a Memory Allocator that operates across the processes by using Inter-process shared memory.
> 
> --chris
>  
> 
> 
> On Thu, Jun 4, 2015 at 5:57 PM, Gerolf Hoflehner <ghoflehner at apple.com <mailto:ghoflehner at apple.com>> wrote:
> Hi,
> 
> I can see even the homogenous variant of this to be useful. Just having the capability of extracting loops and wrapping them into functions and/or modules could help speeding up performance analysis and experiments. It would also help with testing the basic infrastructure + heterogenous environments.
> 
> 
> Cheers
> Gerolf
> 
>> On Jun 4, 2015, at 5:35 PM, Christos Margiolas <chrmargiolas at gmail.com <mailto:chrmargiolas at gmail.com>> wrote:
>> 
>> Hello All,
>> 
>> The last two months I have been working on the design and implementation of a heterogeneous execution engine for LLVM. I started this project as an intern at the Qualcomm Innovation Center and I believe it can be useful to different people and use cases. I am planning to share more details and a set of patches in the next 
>> days. However, I would first like to see if there is an interest for this. 
>> 
>> The project is about providing compiler and runtime support for the automatic and transparent offloading of loop or function workloads to accelerators. 
>> 
>> It is composed of the following:
>> a) Compiler and Transformation Passes for extracting loops or functions for offloading.
>> b) A runtime library that handles scheduling, data sharing and coherency between the
>> host and accelerator sides.
>> c) A modular codebase and design. Adaptors specialize the code transformations for the target accelerators. Runtime plugins manage the interaction with the different accelerator environments.
>> 
>> So far, this work so far supports the Qualcomm DSP accelerator  but I am planning to extend it to support OpenCL accelerators. I have also developed a debug port where I can test the passes and the runtime without requiring an accelerator.
>> 
>> 
>> The project is still in early R&D stage and I am looking forward for feedback and to gauge  the interest level. I am willing to continue working on this as an open source project and bring it to the right shape so it can be merged with the LLVM tree. 
>> 
>> 
>> Regards,
>> Chris
>> 
>> P.S. I intent to join the llvm social in Bay Area tonight and I will be more than happy to talk about it.
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> 

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