From f64c91aeb504c7d57d6bb2418cd6547da2d14dda Mon Sep 17 00:00:00 2001
From: Rob van Nieuwpoort <nieuwpoort@astron.nl>
Date: Tue, 29 Sep 2009 14:56:15 +0000
Subject: [PATCH] Bug 1198: referenties
---
doc/papers/2010/SPM/spm.tex | 86 ++++++++++++++++++-------------------
1 file changed, 43 insertions(+), 43 deletions(-)
diff --git a/doc/papers/2010/SPM/spm.tex b/doc/papers/2010/SPM/spm.tex
index 358b5173987..6e36c67d757 100644
--- a/doc/papers/2010/SPM/spm.tex
+++ b/doc/papers/2010/SPM/spm.tex
@@ -593,12 +593,12 @@ strategies.
On many-core architectures, the memory bandwidth is shared between the
cores. This has shifted the balance between between computational and
-memory performance. The available memory bandwidth per operation has
+memory performance. The available memory bandwidth \emph{per operation} has
decreased dramatically compared to traditional processors. For the
many-core architectures we use here, the theoretical bandwidth per operation is
3--10 times lower than on the BG/P, for instance. In practice, if algorithms
are not optimized well for many-core platforms, the achieved memory bandwidth can
-easily be a hundred times lower than the theoretical maximum.
+easily be ten to a hundred times lower than the theoretical maximum.
Therefore, we must
treat memory bandwidth as a scarce resource, and it is important to
minimize the number of memory accesses. In fact, one of the most
@@ -640,53 +640,53 @@ communication & DMA between SPEs & independent thread
\subsubsection{Well-known memory optimization techniques}
-The insight that optimizing the interaction with the memory system is becoming more and more important
-is not new. The book by Catthoor et al.~\cite{data-access} is an
-excellent starting point for more information on memory-system related
-optimizations. The authors focus on multimedia applications, but the
-techniques described there are also applicable to the field of signal
-processing, which has many similarities to multimedia.
-
-We can
-make a distinction between hardware and software memory optimization techniques.
-The software techniques can be divided further into compiler optimizations and
-algorithmic improvements.
-Examples of hardware-based techniques include caching, data
-prefetching and pipelining. The distinction between hardware and
-software is not entirely black and white. Data prefetching, for instance,
-can be done both in harware and software.
-Another good example is the
-explicit cache of the Cell/B.E. processor. This can be seen as an
-architecture where the programmer handles the cache replacement
-policies instead of the hardware.
+The insight that optimizing the interaction with the memory system is
+becoming more and more important is not new. The book by Catthoor et
+al.~\cite{data-access} is an excellent starting point for more
+information on memory-system related optimizations.
+%The authors focus
+%on multimedia applications, but the techniques described there are
+%also applicable to the field of signal processing, which has many
+%similarities to multimedia.
+
+We can make a distinction between hardware and software memory
+optimization techniques. Examples of hardware-based techniques include caching, data
+prefetching and pipelining. The software techniques can be divided
+further into compiler optimizations and algorithmic improvements.
+ The distinction between hardware and
+software is not entirely black and white. Data prefetching, for
+instance, can be done both in harware and software. Another good
+example is the explicit cache of the \mbox{Cell/B.E.} processor. It can be
+seen as an architecture where the programmer handles the cache
+replacement policies instead of the hardware.
Many optimizations focus on utilizing data caches more efficiently.
Hardware cache hierarchies are in principle transparent for the
application. Nevertheless, it is important to take the sizes of the
-different cache levels into account when optimizing an algorithm.
-A cache line is the smallest unit of memory than can be transferred
-between the main memory and the cache.
-Code can be optimized for the size of the cache lines of a particular architecture.
-Moreover, the associativity of
-the cache can be important. If a cache is N-way set associative, this
-means that any particular location in memory can be cached in either
-of N locations in the data cache. Algorithms can be designed such that
-they take care that cache lines that are needed later are not
-replaced prematurely. Finally, prefetching can be used to load data into caches
-or registers ahead of time.
+different cache levels into account when optimizing an algorithm. A
+cache line is the smallest unit of memory than can be transferred
+between the main memory and the cache. Code can be optimized for the
+cache line size of a particular architecture. Moreover, the
+associativity of the cache can be important. If a cache is N-way set
+associative, this means that any particular location in memory can be
+cached in either of N locations in the data cache. Algorithms can be
+designed such that they take care that cache lines that are needed
+later are not replaced prematurely. Finally, prefetching can be used
+to load data into caches or registers ahead of time.
Many cache-related optimization techniques have been described in the
literature, both in the context of hardware and software. For instance,
an efficient implementation of hardware-based prefetching is described
in~\cite{Chen95effectivehardware-based}. As we will describe in
-Section~\ref{sec:optimizing}, we implemented prefetching manually in the code, for
-example by using multi-buffering on the Cell/B.E., or by explicitly
+Section~\ref{sec:optimizing}, we implemented prefetching manually in software, for
+example by using multi-buffering on the \mbox{Cell/B.E.}, or by explicitly
loading data into shared memory or registers on the GPUs. A good
starting point for cache-aware or cache-oblivious algorithms
is~\cite{cache}. Another good example of a technique that we used to
-improve cache efficiencies for the correlator is the padding of arrays
+improve cache efficiencies for the correlator is the padding of multi-dimensional arrays
with extra ``dummy'' data elements. This way, we can make sure that
-cache replacement policies work well. This well-known technique
+cache replacement policies work well, and subsequent elements in an array dimension are not mapped
+onto the same cache location. This well-known technique
is described, for instance, by Bacon et al.~\cite{cache-tlb-compiler}.
Many additional data access patterns optimization techniques are described
in~\cite{data-access}.
@@ -703,13 +703,13 @@ placement of variables, objects and arrays in
memory~\cite{Panda96memorydata}.
The memory systems of the many-core architectures are quite
-complex. On the GPUs, for instance, several levels of texture cache
-are available, in addition to local memory, and application-managed
-shared memory in several banks. than cannot be accessed
-concurrently. There also are complex interactions between the memory
-system and the hardware thread scheduler that tries to overlap memory
-latencies. GPUs literally run tens of thousands of parallel threads
-to keep all functional units fully occupied. We apply the techniques described
+complex. GPUs, for instance, have banked device memory, several levels of texture cache,
+in addition to local memory, and application-managed
+shared memory (also divided over several banks).
+There also are complex interactions between the memory
+system and the hardware thread scheduler.
+GPUs literally run tens of thousands of parallel threads
+to overlap memory latencies, trying to keep all functional units fully occupied. We apply the techniques described
above in software by hand, since we found that the current compilers
for the many-core architectures do not (yet) implement them well on
their complex memory systems.
--
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