Date: Fri, 16 May 2014 03:05:53 +0000 (UTC) From: Ed Maste <emaste@FreeBSD.org> To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: svn commit: r266208 - head/usr.sbin/pmcstat Message-ID: <201405160305.s4G35ro0067510@svn.freebsd.org>
next in thread | raw e-mail | index | archive | help
Author: emaste Date: Fri May 16 03:05:53 2014 New Revision: 266208 URL: http://svnweb.freebsd.org/changeset/base/266208 Log: 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: head/usr.sbin/pmcstat/pmcstat_log.c Modified: head/usr.sbin/pmcstat/pmcstat_log.c ============================================================================== --- head/usr.sbin/pmcstat/pmcstat_log.c Fri May 16 02:21:51 2014 (r266207) +++ head/usr.sbin/pmcstat/pmcstat_log.c Fri May 16 03:05:53 2014 (r266208) @@ -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); }
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?201405160305.s4G35ro0067510>