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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