Re: [pocl-devel] Unexpected results when running OpenCL kernels with pocl

[Pekka J. <pek...@tu...>]

Hi Matthias,

Lately the reported issues have been more often race conditions or other
bugs in the application side code rather than bugs in PoCL. These can
appear as the program working as expected (by luck) in one OpenCL
platform, but not the other.

Can you try with the latest version (3.0-RC1) and the latest LLVM
to see if there's any difference? If it fails, a simplified reproducer
is needed to track the issue - otherwise it's only guesswork.

BR,
Pekka

On 5/20/22 00:56, Matthias Bock wrote:
> Hi,
> 
> I am experiencing an incorrect behaviour
> when running OpenCL kernels via pocl:
> 
> I wrote an application in C/C++
> calling kernels written in OpenCL C.
> It is a numerical simulation of the propagation
> of an electrical stimulus on tissue,
> from point to point on a 3D mesh
> with thousands of points.
> 
> On one computer I run it
> with Intel's Open Source Beignet driver
> on an Ivy Bridge GT2 featuring 16 compute units.
> Calculation is time consuming, but the results are good:
> A wavefront of excitation forms and travels across
> the mesh as one would expect.
> 
> When I run the identical source code with pocl
> on a machine featuring a Xeon L5640 showing 23 compute units,
> the results are completely different i.e. incorrect:
> The stimulus is not propagating in a wavefront,
> but instead wanders in random lines across the mesh.
> 
> The platform is
> OpenCL 1.2 pocl 1.6, None+Asserts, LLVM 9.0.1,
> RELOC, SLEEF, DISTRO, POCL_DEBUG.
> The device is
> pthread-Intel(R) Xeon(R) CPU  L5640  @ 2.27GHz
> OpenCL 1.2 pocl HSTR: pthread-x86_64-pc-linux-gnu-westmere.
> 
> Unfortunately, I can't share the original source code,
> but I suspect some sort of race condition or the
> queue not being executed in the correct order.
> Inserting global memory barriers in all kernels
> and adding queue flush & finish calls
> in the main program after every kernel call
> didn't change anything though.
> 
> Do you have any ideas or suggestions?
> 
> Cheers,
> Matthias
> 
> 
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