Commit f92a3699 authored by Philippe Helluy's avatar Philippe Helluy

up

parent 5c26900e
......@@ -411,6 +411,548 @@ I would like the authors to give a more detailed explanation of how they
\begin_inset Quotes erd
\end_inset
:
\begin_inset Newline newline
\end_inset
We enriched the computational part of the part with a more precise evaluation
of the performance of the code: memory bandwidth and computational intensity.
This analysis confirms the excellent efficiency of the implementation.
\begin_inset Formula
\[
n_{\text{GB}}=\frac{\texttt{\texttt{Nx}\ensuremath{\times\texttt{Ny}}\ensuremath{\times prec}}\times4\times m}{1024^{3}},
\]
\end_inset
where
\begin_inset Formula $prec$
\end_inset
is the number of bytes for storing one floating point number (
\begin_inset Formula $prec=4$
\end_inset
for single precision and
\begin_inset Formula $prec=8$
\end_inset
for double precision).
We then perform a given number of time iterations niter and measure the
elapsed time
\begin_inset Formula $t_{\text{elapsed}}$
\end_inset
(with a specific features of the OpenCL library).
We perform two kind of experiments.
In the first experiment, we deactivate the numerical computations and only
perform the shift operations.
The memory bandwidth of the shift algorithm is then given by
\begin_inset Formula
\[
b=\frac{2\times n_{\text{GB}}\times niter}{t_{\text{elapsed}}}.
\]
\end_inset
In the second experiment, we reactivate the computations and measure how
the bandwidth is reduced.
This allows to evaluating how the elapsed time is shared between memory
transfers and computations.
The results are given in Table xxx
\begin_inset Newline newline
\end_inset
\begin_inset Tabular
<lyxtabular version="3" rows="10" columns="5">
<features tabularvalignment="middle">
<column alignment="center" valignment="top">
<column alignment="center" valignment="top">
<column alignment="center" valignment="top">
<column alignment="center" valignment="top">
<column alignment="center" valignment="top">
<row>
<cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" usebox="none">
\begin_inset Text
\begin_layout Plain Layout
\end_layout
\end_inset
</cell>
<cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" usebox="none">
\begin_inset Text
\begin_layout Plain Layout
prec.
\end_layout
\end_inset
</cell>
<cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" usebox="none">
\begin_inset Text
\begin_layout Plain Layout
\begin_inset Formula $b$
\end_inset
(GB/s, only shift)
\end_layout
\end_inset
</cell>
<cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" usebox="none">
\begin_inset Text
\begin_layout Plain Layout
\begin_inset Formula $b$
\end_inset
(GB/s, full LBM)
\end_layout
\end_inset
</cell>
<cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" rightline="true" usebox="none">
\begin_inset Text
\begin_layout Plain Layout
max.
bandwidth (GB/s)
\end_layout
\end_inset
</cell>
</row>
<row>
<cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">
\begin_inset Text
\begin_layout Plain Layout
AMD
\end_layout
\end_inset
</cell>
<cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">
\begin_inset Text
\begin_layout Plain Layout
float32
\end_layout
\end_inset
</cell>
<cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">
\begin_inset Text
\begin_layout Plain Layout
\end_layout
\end_inset
</cell>
<cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">
\begin_inset Text
\begin_layout Plain Layout
\end_layout
\end_inset
</cell>
<cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none">
\begin_inset Text
\begin_layout Plain Layout
\end_layout
\end_inset
</cell>
</row>
<row>
<cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">
\begin_inset Text
\begin_layout Plain Layout
AMD
\end_layout
\end_inset
</cell>
<cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">
\begin_inset Text
\begin_layout Plain Layout
float32
\end_layout
\end_inset
</cell>
<cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">
\begin_inset Text
\begin_layout Plain Layout
\end_layout
\end_inset
</cell>
<cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">
\begin_inset Text
\begin_layout Plain Layout
\end_layout
\end_inset
</cell>
<cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none">
\begin_inset Text
\begin_layout Plain Layout
\end_layout
\end_inset
</cell>
</row>
<row>
<cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">
\begin_inset Text
\begin_layout Plain Layout
Iris 640
\end_layout
\end_inset
</cell>
<cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">
\begin_inset Text
\begin_layout Plain Layout
float32
\end_layout
\end_inset
</cell>
<cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">
\begin_inset Text
\begin_layout Plain Layout
26.20
\end_layout
\end_inset
</cell>
<cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">
\begin_inset Text
\begin_layout Plain Layout
24.98
\end_layout
\end_inset
</cell>
<cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none">
\begin_inset Text
\begin_layout Plain Layout
\end_layout
\end_inset
</cell>
</row>
<row>
<cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">
\begin_inset Text
\begin_layout Plain Layout
Iris 640
\end_layout
\end_inset
</cell>
<cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">
\begin_inset Text
\begin_layout Plain Layout
float64
\end_layout
\end_inset
</cell>
<cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">
\begin_inset Text
\begin_layout Plain Layout
\end_layout
\end_inset
</cell>
<cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">
\begin_inset Text
\begin_layout Plain Layout
\end_layout
\end_inset
</cell>
<cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none">
\begin_inset Text
\begin_layout Plain Layout
\end_layout
\end_inset
</cell>
</row>
<row>
<cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">
\begin_inset Text
\begin_layout Plain Layout
GTX
\end_layout
\end_inset
</cell>
<cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">
\begin_inset Text
\begin_layout Plain Layout
float32
\end_layout
\end_inset
</cell>
<cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">
\begin_inset Text
\begin_layout Plain Layout
\end_layout
\end_inset
</cell>
<cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">
\begin_inset Text
\begin_layout Plain Layout
\end_layout
\end_inset
</cell>
<cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none">
\begin_inset Text
\begin_layout Plain Layout
\end_layout
\end_inset
</cell>
</row>
<row>
<cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">
\begin_inset Text
\begin_layout Plain Layout
Quadro
\end_layout
\end_inset
</cell>
<cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">
\begin_inset Text
\begin_layout Plain Layout
float32
\end_layout
\end_inset
</cell>
<cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">
\begin_inset Text
\begin_layout Plain Layout
\end_layout
\end_inset
</cell>
<cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">
\begin_inset Text
\begin_layout Plain Layout
\end_layout
\end_inset
</cell>
<cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none">
\begin_inset Text
\begin_layout Plain Layout
\end_layout
\end_inset
</cell>
</row>
<row>
<cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">
\begin_inset Text
\begin_layout Plain Layout
Quadro
\end_layout
\end_inset
</cell>
<cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">
\begin_inset Text
\begin_layout Plain Layout
float64
\end_layout
\end_inset
</cell>
<cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">
\begin_inset Text
\begin_layout Plain Layout
\end_layout
\end_inset
</cell>
<cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">
\begin_inset Text
\begin_layout Plain Layout
\end_layout
\end_inset
</cell>
<cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none">
\begin_inset Text
\begin_layout Plain Layout
\end_layout
\end_inset
</cell>
</row>
<row>
<cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">
\begin_inset Text
\begin_layout Plain Layout
V100
\end_layout
\end_inset
</cell>
<cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">
\begin_inset Text
\begin_layout Plain Layout
float32
\end_layout
\end_inset
</cell>
<cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">
\begin_inset Text
\begin_layout Plain Layout
\end_layout
\end_inset
</cell>
<cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">
\begin_inset Text
\begin_layout Plain Layout
\end_layout
\end_inset
</cell>
<cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none">
\begin_inset Text
\begin_layout Plain Layout
\end_layout
\end_inset
</cell>
</row>
<row>
<cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" usebox="none">
\begin_inset Text
\begin_layout Plain Layout
V100
\end_layout
\end_inset
</cell>
<cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" usebox="none">
\begin_inset Text
\begin_layout Plain Layout
float64
\end_layout
\end_inset
</cell>
<cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" usebox="none">
\begin_inset Text
\begin_layout Plain Layout
\end_layout
\end_inset
</cell>
<cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" usebox="none">
\begin_inset Text
\begin_layout Plain Layout
\end_layout
\end_inset
</cell>
<cell alignment="center" valignment="top" topline="true" bottomline="true" leftline="true" rightline="true" usebox="none">
\begin_inset Text
\begin_layout Plain Layout
\end_layout
\end_inset
</cell>
</row>
</lyxtabular>
\end_inset
\end_layout
......
......@@ -1714,7 +1714,7 @@ MRREVIEWER = {Philip D. Loewen},
}
@article{toth2000b,
title={The∇{\textperiodcentered} B= 0 constraint in shock-capturing magnetohydrodynamics codes},
title={The $\nabla \cdot b= 0$ constraint in shock-capturing magnetohydrodynamics codes},
author={T{\'o}th, G{\'a}bor},
journal={Journal of Computational Physics},
volume={161},
......
......@@ -865,6 +865,15 @@ $
\texttt{nvtop}\footnote{\url{https://github.com/Syllo/nvtop}} indicates
that the GPU occupation is of $99\%$. This indicates a quasi-optimal
implementation.
In order to measure the efficiency of the implementation we perform a memory bandwidth test
on several grid sizes. One time step of the method implies the read access in the global memory
to the set of fields of the previous time step. The local computations are done in registers. Then
there is another write access to global memory for storing the data of the next time step.
The size in memory in Gigabyte of one set of fields is
$$
n_{\text{GB}}=\frac{\texttt{\texttt{Nx}\ensuremath{\times}\texttt{Ny}\ensuremath{\times b}}\times4\times m}{1024^{3}}
,$$
where $b$ is the number of bytes for storing one floating point number ($b=4$ for single precision and $b=8$ for double precision),
\section{Numerical applications to MHD}
......
......@@ -166,6 +166,10 @@ def solve_ocl(m=_m, n=_n, nx=_nx, ny=_ny, Lx=_Lx, Ly=_Ly, Tmax=_Tmax,
levels=np.linspace(_minplot, _maxplot, 16))
#fig = Figure(title=plot_title)
compute = False
print("Compute:")
print(compute)
print("start OpenCL computations...")
while t < Tmax + dt:
......@@ -199,7 +203,10 @@ def solve_ocl(m=_m, n=_n, nx=_nx, ny=_ny, Lx=_Lx, Ly=_Ly, Tmax=_Tmax,
t += dt
#event = prg.time_step(queue, (nx * ny, ), None, wn_gpu, wnp1_gpu)
event = prg.time_step(queue, (nx * ny, ), None, fn_gpu, fnp1_gpu)
if compute :
event = prg.time_step(queue, (nx * ny, ), None, fn_gpu, fnp1_gpu)
else :
event = prg.time_shift(queue, (nx * ny, ), None, fn_gpu, fnp1_gpu)
#event = prg.time_step(queue, (nx * ny, ), None, wn_gpu, wnp1_gpu, wait_for = [event])
event.wait()
queue.finish()
......
Markdown is supported
0% or .
You are about to add 0 people to the discussion. Proceed with caution.
Finish editing this message first!
Please register or to comment