Date: Fri, 23 May 2014 17:46:00 +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-10@freebsd.org Subject: svn commit: r266590 - stable/10/usr.sbin/pmcstat Message-ID: <201405231746.s4NHk0iJ062034@svn.freebsd.org>
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Author: emaste Date: Fri May 23 17:46:00 2014 New Revision: 266590 URL: http://svnweb.freebsd.org/changeset/base/266590 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%. Modified: stable/10/usr.sbin/pmcstat/pmcstat_log.c Directory Properties: stable/10/ (props changed) Modified: stable/10/usr.sbin/pmcstat/pmcstat_log.c ============================================================================== --- stable/10/usr.sbin/pmcstat/pmcstat_log.c Fri May 23 16:46:50 2014 (r266589) +++ stable/10/usr.sbin/pmcstat/pmcstat_log.c Fri May 23 17:46:00 2014 (r266590) @@ -307,10 +307,10 @@ 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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