Date: Thu, 12 Jun 2014 17:08:04 +0000 (UTC) From: Ed Maste <emaste@FreeBSD.org> To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-stable@freebsd.org, svn-src-stable-9@freebsd.org Subject: svn commit: r267415 - stable/9/usr.sbin/pmcstat Message-ID: <201406121708.s5CH84Ef049261@svn.freebsd.org>
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Author: emaste Date: Thu Jun 12 17:08:04 2014 New Revision: 267415 URL: http://svnweb.freebsd.org/changeset/base/267415 Log: MFC r266208: Speed up pmcstat by improving string hash In one case generating callgraph output from a 24MB system-wide sampling data file took 17.4 seconds on average. Profiling showed pmcstat spending a lot of time in strcmp, due to hash collisions. Replacing the XOR-only hash with FNV-1a reduces the run time for my test by 40%. Approved by: re Modified: stable/9/usr.sbin/pmcstat/pmcstat_log.c Directory Properties: stable/9/usr.sbin/pmcstat/ (props changed) Modified: stable/9/usr.sbin/pmcstat/pmcstat_log.c ============================================================================== --- stable/9/usr.sbin/pmcstat/pmcstat_log.c Thu Jun 12 17:06:50 2014 (r267414) +++ stable/9/usr.sbin/pmcstat/pmcstat_log.c Thu Jun 12 17:08:04 2014 (r267415) @@ -301,10 +301,10 @@ pmcstat_stats_reset(int reset_global) static int pmcstat_string_compute_hash(const char *s) { - int hash; + unsigned hash; - for (hash = 0; *s; s++) - hash ^= *s; + for (hash = 2166136261; *s; s++) + hash = (hash ^ *s) * 16777619; return (hash & PMCSTAT_HASH_MASK); }
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