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New GPU comments and sample program in docs.
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Salvatore Filippone
+159
-18
@@ -419,41 +419,182 @@ call P%build(A,desc_A,info)
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\subsection{GPU example\label{sec:gpu-example}}
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The code reported in Figure~\ref{fig:gpu-ex1} shows how to set up a
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The code discussed here shows how to set up a
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program exploiting the combined GPU capabilities of PSBLAS and
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AMG4PSBLAS.
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AMG4PSBLAS. The code example is availabile in the source distribution
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directory \verb|amg4psblas/tests/gpu|.
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First of all, we need to include the appropriate modules and
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declare some auxiliary variables:
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\begin{listing}[h!]
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\ifpdf
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\begin{minted}[breaklines=true,bgcolor=bg,fontsize=\small]{fortran}
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! build a one-level RAS with overlap 2 and ILU(0) on the local blocks.
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call P%init('AS',info)
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call P%set('SUB_OVR',2,info)
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call P%build(A,desc_A,info)
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... ...
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! solve Ax=b with preconditioned BiCGSTAB
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call psb_krylov('BICGSTAB',A,P,b,x,tol,desc_A,info)
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program amg_d_pde3d
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use psb_base_mod
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use amg_prec_mod
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use psb_krylov_mod
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use psb_util_mod
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use psb_gpu_mod
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use data_input
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use amg_d_pde3d_base_mod
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use amg_d_pde3d_exp_mod
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use amg_d_pde3d_gauss_mod
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use amg_d_genpde_mod
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implicit none
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.......
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! GPU variables
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type(psb_d_hlg_sparse_mat) :: agmold
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type(psb_d_vect_gpu) :: vgmold
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type(psb_i_vect_gpu) :: igmold
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\end{minted}
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\else
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\begin{center}
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\begin{minipage}{.90\textwidth}
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{\small
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\begin{verbatim}
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! build a one-level RAS with overlap 2 and ILU(0) on the local blocks.
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call P%init('AS',info)
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call P%set('SUB_OVR',2,info)
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call P%build(A,desc_A,info)
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... ...
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! solve Ax=b with preconditioned BiCGSTAB
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call psb_krylov('BICGSTAB',A,P,b,x,tol,desc_A,info)
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\end{verbatim}
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program amg_d_pde3d
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use psb_base_mod
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use amg_prec_mod
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use psb_krylov_mod
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use psb_util_mod
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use psb_gpu_mod
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use data_input
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use amg_d_pde3d_base_mod
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use amg_d_pde3d_exp_mod
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use amg_d_pde3d_gauss_mod
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use amg_d_genpde_mod
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implicit none
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.......
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! GPU variables
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type(psb_d_hlg_sparse_mat) :: agmold
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type(psb_d_vect_gpu) :: vgmold
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type(psb_i_vect_gpu) :: igmold
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\end{verbatim}
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}
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\end{minipage}
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\end{center}
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\fi
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\caption{setup of a one-level Schwarz preconditioner.\label{fig:gpu-ex1}}
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\caption{setup of a GPU-enabled test program part one.\label{fig:gpu-ex1}}
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\end{listing}
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We then have to initialize the GPU environment, and pass the
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appropriate MOLD variables to the build methods
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\begin{listing}[h!]
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\ifpdf
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\begin{minted}[breaklines=true,bgcolor=bg,fontsize=\small]{fortran}
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call psb_init(ctxt)
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call psb_info(ctxt,iam,np)
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!
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! BEWARE: if you have NGPUS per node, the default is to
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! attach to mod(IAM,NGPUS)
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!
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call psb_gpu_init(ictxt)
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......
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t1 = psb_wtime()
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call prec%smoothers_build(a,desc_a,info, amold=agmold, vmold=vgmold, imold=igmold)
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\end{minted}
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\else
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\begin{center}
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\begin{minipage}{.90\textwidth}
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{\small
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\begin{verbatim}
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call psb_init(ctxt)
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call psb_info(ctxt,iam,np)
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!
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! BEWARE: if you have NGPUS per node, the default is to
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! attach to mod(IAM,NGPUS)
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!
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call psb_gpu_init(ictxt)
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......
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t1 = psb_wtime()
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call prec%smoothers_build(a,desc_a,info, amold=agmold, vmold=vgmold, imold=igmold)
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\end{verbatim}
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}
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\end{minipage}
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\end{center}
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\fi
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\caption{setup of a GPU-enabled test program part two.\label{fig:gpu-ex2}}
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\end{listing}
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Finally, we convert the input matrix, the descriptor and the vectors,
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then preallocate the preconditioner workspace before entering the
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Krylov method. At the end of the code, we close the GPU environment
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\begin{listing}[h!]
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\ifpdf
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\begin{minted}[breaklines=true,bgcolor=bg,fontsize=\small]{fortran}
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call desc_a%cnv(mold=igmold)
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call a%cscnv(info,mold=agmold)
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call psb_geasb(x,desc_a,info,mold=vgmold)
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call psb_geasb(b,desc_a,info,mold=vgmold)
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!
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! iterative method parameters
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!
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call psb_barrier(ctxt)
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call prec%allocate_wrk(info)
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t1 = psb_wtime()
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call psb_krylov(s_choice%kmethd,a,prec,b,x,s_choice%eps,&
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& desc_a,info,itmax=s_choice%itmax,iter=iter,err=err,itrace=s_choice%itrace,&
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& istop=s_choice%istopc,irst=s_choice%irst)
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call prec%deallocate_wrk(info)
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call psb_barrier(ctxt)
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tslv = psb_wtime() - t1
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......
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call psb_gpu_exit()
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call psb_exit(ctxt)
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stop
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\end{minted}
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\else
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\begin{center}
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\begin{minipage}{.90\textwidth}
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{\small
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\begin{verbatim}
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call desc_a%cnv(mold=igmold)
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call a%cscnv(info,mold=agmold)
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call psb_geasb(x,desc_a,info,mold=vgmold)
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call psb_geasb(b,desc_a,info,mold=vgmold)
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!
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! iterative method parameters
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!
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call psb_barrier(ctxt)
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call prec%allocate_wrk(info)
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t1 = psb_wtime()
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call psb_krylov(s_choice%kmethd,a,prec,b,x,s_choice%eps,&
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& desc_a,info,itmax=s_choice%itmax,iter=iter,err=err,itrace=s_choice%itrace,&
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& istop=s_choice%istopc,irst=s_choice%irst)
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call prec%deallocate_wrk(info)
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call psb_barrier(ctxt)
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tslv = psb_wtime() - t1
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......
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call psb_gpu_exit()
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call psb_exit(ctxt)
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stop
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\end{verbatim}
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}
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\end{minipage}
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\end{center}
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\fi
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\caption{setup of a GPU-enabled test program part three.\label{fig:gpu-ex3}}
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\end{listing}
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It is very important to employ solvers that are suited
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to the GPU, i.e. solvers that do NOT employ triangular
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system solve kernels. Solvers that satisfy this constraint include:
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\begin{itemize}
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\item \verb|JACOBI|
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\item \verb|INVK|
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\item \verb|INVT|
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\item \verb|AINV|
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\end{itemize}
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and their \verb|L1| variants.
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%%% Local Variables:
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%%% mode: latex
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