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    <p>I found <a href="http://oprofile.sourceforge.net" rel="nofollow noreferrer">oprofile</a> to be a lot better option than gprof for profiling, in this situation. The <a href="http://oprofile.sourceforge.net/examples/" rel="nofollow noreferrer">reports from oprofile</a> are much more comprehensive. I compiled out the ruby portions which were causing the seg-faults (not all of them were), from the C extension using #ifndef PROFILE, and replaced them with non-ruby code. I wrote a main() routine within the extension itself, to call the functions in the extension. Then I set up a makefile to compile the extension as a C program with PROFILE defined. Then I <a href="http://lbrandy.com/blog/2008/11/oprofile-profiling-in-linux-for-fun-and-profit/" rel="nofollow noreferrer">installed oprofile on Ubuntu</a>. Wrote this script.</p> <pre><code>#!/bin/bash sudo opcontrol --reset sudo opcontrol --start ./a.out Rome Damascus NewYork Delhi Bangalore sudo opcontrol --shutdown opreport -lt1 </code></pre> <p>Compiled my program, and executed the above script, which gives output like this from the "opreport" command:</p> <pre><code>... ... Killing daemon. warning: /no-vmlinux could not be found. warning: [vdso] (tgid:10675 range:0x920000-0x921000) could not be found. warning: [vdso] (tgid:1270 range:0xba1000-0xba2000) could not be found. warning: [vdso] (tgid:1675 range:0x973000-0x974000) could not be found. warning: [vdso] (tgid:1711 range:0x264000-0x265000) could not be found. warning: [vdso] (tgid:1737 range:0x990000-0x991000) could not be found. warning: [vdso] (tgid:2477 range:0xa53000-0xa54000) could not be found. warning: [vdso] (tgid:5658 range:0x7ae000-0x7af000) could not be found. CPU: Core Solo / Duo, speed 1000 MHz (estimated) Counted CPU_CLK_UNHALTED events (Unhalted clock cycles) with a unit mask of 0x00 (Unhalted core cycles) count 100000 samples % app name symbol name 12731 32.8949 a.out levenshtein 11958 30.8976 a.out corpora_pass2 5231 13.5161 no-vmlinux /no-vmlinux 4021 10.3896 a.out corpora_pass1 1733 4.4778 libc-2.10.1.so /lib/tls/i686/cmov/libc-2.10.1.so 542 1.4004 ld-2.10.1.so /lib/ld-2.10.1.so 398 1.0284 a.out method_top_matches </code></pre> <p>There it is: the top consumer is the function levenshtein(). I followed this by another command to generate disassembled output annotated with source code and execution count/time of each line. This looks like this (counts/times are on the left of each executed line):</p> <pre><code>&gt; opannotate --source --assembly ./a.out &gt; report.as.handcoded.1 &gt; cat report.as.handcoded.1 ... ... ... : __asm__ ( 2 0.0069 : 804918a: mov -0x50(%ebp),%ecx 4 0.0137 : 804918d: mov -0x54(%ebp),%ebx : 8049190: mov -0x4c(%ebp),%eax 12 0.0412 : 8049193: cmp %eax,%ecx 10 0.0344 : 8049195: cmovbe %ecx,%eax 8 0.0275 : 8049198: cmp %eax,%ebx 11 0.0378 : 804919a: cmovbe %ebx,%eax 16 0.0550 : 804919d: mov %eax,-0x4c(%ebp) : "cmp %0, %2\n\t" : "cmovbe %2, %0\n\t" : : "+r"(a) : : "%r"(b), "r"(c) : ); : return a; ... ... ... </code></pre>
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