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@@ -237,6 +237,11 @@ HDF5 Technical Notes&nbsp;&nbsp;
     Results of reviewing tests for API functions.
 </td></tr>
 
+<tr><td valign=top><a href="TechNotes/Basic_perform.html">Basic Performance Tools</a>
+    </td><td>&nbsp;</td><td valign=top>
+    A description of the three basic performance tools (chunk, iopipe, overhead).
+</td></tr>
+
 <tr><td valign=top><a href="TechNotes/VLTypes.html">Variable-Length Datatype Info</a>
     </td><td>&nbsp;</td><td valign=top>
     Description of various aspects of using variable-length datatypes in HDF5.
@@ -286,7 +291,7 @@ HDF5 Technical Notes&nbsp;&nbsp;
 Describes HDF5 Release 1.6.0, July 2003
 </address><!-- #EndLibraryItem -->
 
-Last modified:  16 November 2002
+Last modified:  25 September 2003
 
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+<!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML//EN">
+<html>
+  <head>
+    <title>Description of the three basic performance tools</title>
+  </head>
+
+  <body>
+    <h1>Description of the three basic performance tools</h1>
+
+    <h2>iopipe</h2>
+  <p>Times reads and writes to an HDF5 2-d dataset and compares that with
+  reads and writes using POSIX I/O.  Reports seven measurements in
+  terms of CPU user time, CPU system time, elapsed time, and
+  bandwidth:
+
+
+<DL>
+<DD>fill raw: time it takes to memset() a buffer.</DD>
+<DD> fill hdf5: time it takes to read from a dataset never written</DD>
+<DD>out raw: time it takes to write using POSIX I/O</DD>
+<DD>out hdf5: time it takes to write using H5Dwrite()</DD>
+<DD>in raw: time it takes to read data just written using POSIX I/O</DD>
+<DD>in hdf5: time it takes to H5Dread() data written with H5Dwrite()</DD>
+<DD>in hdf5 partial: time it takes to H5Dread() the "center" area.</DD>
+</DL>
+
+
+  <p>This is a pretty stupid performance test. It accesses the same area
+  of file and memory over and over and the file size is way too
+  small. But it is good at showing how much overhead there is in the
+  library itself.
+
+
+    <h2>chunk</h2>
+  <p>Determines how efficient the raw data cache is for various access
+  patterns of a chunked dataset, both reading and writing.  The access
+  pattern is either (a) we access the entire dataset by moving a window
+  across and down a 2-d dataset in row-major order a full window
+  height and width at a time, or (b) we access part of a dataset by moving
+  the window diagonally from the (0,0) corner to the opposite corner
+  by half the window height and width at a time. The window is
+  measured in terms of the chunk size.
+
+
+  <p>The result is:
+    <br>A table written to stdout that contains the window size as a
+    fraction of the chunk size and the efficiencey of the cache (i.e.,
+    number of bytes accessed by H5Dread() or H5Dwrite() divided by the
+    number of bytes of the dataset actually read or written by lower
+    layers.
+
+
+    <p>A gnuplot script and data files which can be displayed by running
+    gnuplot and typing the command `load "x-gnuplot"'.
+
+
+    <h2>overhead</h2>
+  <p>Measures the overhead used by the B-tree for indexing chunked
+  datasets. As data is written to a chunked dataset the B-tree
+  grows and its nodes get split.  When a node splits one of three
+  ratios are used to determine how many items from the original node
+  go into the new left and right nodes, and these ratios affect the
+  total size of the B-tree in a way that depends on the order that
+  data is written to the dataset.
+
+
+  <p>Invoke as `overhead usage' for more information.
+    <hr>
+    <address><a href="mailto:matzke@llnl.gov">Robb Matzke</a></address>
+<!-- Created: Tue Mar 17 11:13:35 EST 1998 -->
+<!-- hhmts start -->
+Last modified: Jun 4, 2003
+<!-- hhmts end -->
+  </body>
+</html>