Modify AMDGPU threads heurisitics

src/ParallelKernel/parallel.jl

@@ -250,7 +250,7 @@ end
 
 function parallel_call_gpu(ranges::Union{Symbol,Expr}, kernelcall::Expr, backend_kwargs_expr::Array, async::Bool, package::Symbol; stream::Union{Symbol,Expr}=default_stream(package), shmem::Union{Symbol,Expr,Nothing}=nothing, launch::Bool=true, configcall::Expr=kernelcall)
     maxsize  = :(length.(ParallelStencil.ParallelKernel.promote_ranges($ranges)))
-    nthreads = :( ParallelStencil.ParallelKernel.compute_nthreads($maxsize) )
+    nthreads = :( ParallelStencil.ParallelKernel.compute_nthreads($maxsize, $package) )
     nblocks  = :( ParallelStencil.ParallelKernel.compute_nblocks($maxsize, $nthreads) )
     parallel_call_gpu(ranges, nblocks, nthreads, kernelcall, backend_kwargs_expr, async, package; stream=stream, shmem=shmem, launch=launch)
 end
@@ -495,9 +495,11 @@ function compute_ranges(maxsize)
     return (1:maxsize[1], 1:maxsize[2], 1:maxsize[3])
 end
 
-function compute_nthreads(maxsize; nthreads_max=NTHREADS_MAX, flatdim=0) # This is a heuristic, which results in (32,8,1) threads, except if maxsize[1] < 32 or maxsize[2] < 8.
+function compute_nthreads(maxsize, package; nthreads_max=NTHREADS_MAX, flatdim=0) # This is a heuristic, which results in (32,8,1) threads, except if maxsize[1] < 32 or maxsize[2] < 8.
     maxsize = promote_maxsize(maxsize)
-    nthreads_x = min(32,                                             (flatdim==1) ? 1 : maxsize[1])
+    if     (package == PKG_CUDA)   nthreads_x = min(32,              (flatdim==1) ? 1 : maxsize[1])
+    elseif (package == PKG_AMDGPU) nthreads_x = min(128,             (flatdim==1) ? 1 : maxsize[1])
+    end
     nthreads_y = min(ceil(Int,nthreads_max/nthreads_x),              (flatdim==2) ? 1 : maxsize[2])
     nthreads_z = min(ceil(Int,nthreads_max/(nthreads_x*nthreads_y)), (flatdim==3) ? 1 : maxsize[3])
     return (nthreads_x, nthreads_y , nthreads_z)