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Date: Tue, 10 Dec 1996 03:27:43 GMTServer: NCSA/1.4.2Content-type: text/htmlLast-modified: Thu, 03 Oct 1996 03:34:42 GMTContent-length: 8085<HTML><HEAD><TITLE>Etch Overview</TITLE><BASE HREF="http://www.cs.washington.edu/homes/bershad/etch/index.html"><META NAME="GENERATOR" CONTENT="Internet Assistant for Microsoft Word 2.0z"></HEAD><BODY bgcolor="#ffffff"><H1>Instrumentation and Optimization of WIN32/Intel Executables</H1><P><B>Etch</B> is an application program performance evaluation andoptimization system, developed for Intel x86 platforms runningWindows/95, Windows/NT and Linux operating systems. The systemallows you annotate existing binaries with arbitrary instructions(for example, to trace, or perform coverage analysis), or to rewritean existing binary so that it executes more efficiently. <P>Etch works directly on x86 executables. It does <EM>not</EM> requireprogram source code for either measurement or optimization. <P><h2> Some Results</H2>If you'd like to see some traces we've generated from a few popularWindows programs on X86, click<A HREF="http://etch.eecs.harvard.edu/traces/index.html">here.</A><H2>Who uses Etch? </H2><P>Etch is targeted at two different user groups: <EM>developers</EM>,who wish to understand the performance of their programs duringthe development cycle, and <EM>users</EM>, who wish to understandand improve the performance of common applications executing intheir environment. <P>Etch provides both groups with measurement tools to evaluate performanceat several levels of detail, and optimization tools to automaticallyrestructure programs to improve performance, where possible. <H2>How Etch Works </H2><P>Etch reads executable binaries (and, under Win32, DLLs) for anapplication, modifies the image, and writes a new one that hasbeen enhanced for measurement or optimization. The transformationsperformed on the binary by Etch do not change program correctness,although a program transformed for performance measurement collectionwill run more slowly. Etch does not require changes to the operatingsystem, but a modified Etch binary may utilize OS facilities,such as software timers, or even implementation-specific facilities,such as Intel Pentium performance counters. <H2>Using Etch </H2><P>There are three key concepts in using Etch: <DL><DT>Instrumentation<DD>Instrumentation transforms a binary according to an arbitrarycriteria. For example, a program may be instrumented to countinstructions, or to count the occurrence of each instruction,or to simulate a cache by tracking memory references. <DT>Data collection<DD>Once instrumented, an executable can be run. At that time,instrumentation routines collect data about the program. <DT>Data processing<DD>Once run, any data generated by an instrumented executablecan be processed. Trace-based optimization is a typical data processingphase made possible by Etch. </DL><H3>Instrumentation </H3><P>To instrument a program, Etch is invoked with the name of an executableand a DLL. The DLL provides a set of routines which are invokedfor each instruction in the executable. Roughly, Etch operatesas: <PRE><FONT SIZE=2> for each instruction in executable InstrumentBefore(instruction); InstrumentAfter(instruction); end; InstrumentBeforeMainProgram(); InstrumentAfterMainProgram(); </FONT></PRE><P>The instrumentation tool provides implementations of these "Before"and "After" functions. The call back functions can inturn direct Etch to modify the executable with respect to thespecific instruction. The directions in effect say "before(or after) this instruction runs, please call some specific functionwith some specific set of arguments." For example, to countinstructions, the InstrumentBefore procedure would direct Etchto insert code that incremented a counter at runtime. These insertedinstructions do not change the correctness of the program. <P>Once the entire executable has been scanned and instrumented,Etch writes a new version of the executable that can be run. Anyfunctions referenced in the callback routines, as well as theEtch runtime library are included in the new executable. <BR><H3>Data Collection </H3><P>The executable written by Etch can be run, and any instrumentationroutines will run as a side effect of running the program. Instrumentationroutines, as the program is running, can inspect the state ofthe program, for example, the contents of registers, or effectiveaddresses. All addresses, whether text or data, are relative tothe original binary, so the collection routines do not have tocompensate for the fact that they are part of a modified executable.<BR><H3>Data Processing </H3><P>When an Etched program terminates, its data collection routinescan save information about the executable to disk. Later, post-processingutilities can examine the data. For example, a predicted executiontime can be determined after the fact based on hypothetical processor,cache, and memory speeds. At a lower level, detailed informationabout a program's performance can be obtained such as is shownbelow in the graph of instruction cache performance for a collectionof popular Win32 programs. The graph shows the miss penaltyof the first level instruction cache and a second level unifiedcache for the Perl interpreter, three commercial C++ compilers,and MS-WORD.<BR><H4><IMG SRC="IMG00001.GIF"><BR></H4><H4>Optimization </H4><P>Etch also provides facilities for rewriting an executable in orderto improve its performance. For example, the instrumentation phase,rather than adding new instructions, can direct Etch to writethe executable out according to a different code layout optimizedfor cache and VM behavior. <H4>The impact of optimization</H4><P>The graph below shows the reduction in instruction cache missesand execution time (in cycles) for a collection of popular Win32programs that have been optimized for code layout using Etch ona 90Mhz Pentium. Etch was first used to discover the programs'locality while executing against a training set, and then rewrittenin order to achieve a tighter cache and VM packing. Infrequentlyexecuted basic blocks were moved out of line, and frequently interactingbasic blocks were laid out contiguously in the executable. Theresults were measured using inputs different than those used duringtraining.<BR><P><IMG SRC="IMG00002.GIF"><BR><H2>The User Interface </H2><P>In addition to a programming interface, Etch also offers a graphicaluser interface for performing common instrumentation and optimizationoperations. The user interface can drive the measurement process:it runs Etch on the original binary to produce a new binary, modifiedto collect the necessary behavioral data; it executes the modifiedbinary to produce the data; and it feeds the data to analysistools that produce graphs or charts that help to pinpoint problems.Once a problem has been identified, the user may instruct Etchto perform a performance-optimization transformation. For example,Etch may rewrite the original binary to change the layout of dataor code in order to improve cache or virtual memory performance. <BR><H3>Sample dialog box from the user interface<BR></H3><P><IMG SRC="IMG00003.GIF"><BR><BR><H3>Sample results showing distribution of instruction opcodes<BR></H3><P><IMG SRC="IMG00004.GIF"><BR><H2>Requirements </H2><P>Etch runs on Intel 486, Pentium and P6 processors with at least 24 MB of memory. Etch works on 32-bit (Win32) binaries. It hasbeen used for programs built by MSVC, Borland, and Intel compilers. <H2>Availability </H2><P>If you are interested in obtaining more information about Etch,please contact <A href="mailto:etch-info@cs.washington.edu">etch-info@cs.washington.edu</A><H2>Project Members </H2><P>Etch is due to the efforts of people at Harvard University andthe University of Washington. These include: Dennis Lee, Ted Romer,Geoff Voelker, Alec Wolman, Wayne Wong, Brad Chen, Brian Bershad,and Hank Levy. </BODY></HTML>⌨️ 快捷键说明
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