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| author | emaste <emaste@FreeBSD.org> | 2014-05-16 03:05:53 +0000 |
|---|---|---|
| committer | emaste <emaste@FreeBSD.org> | 2014-05-16 03:05:53 +0000 |
| commit | 0e1c93d3c1a464c1bcbd9ba493241df58a7d10ad (patch) | |
| tree | 8489ff7f77613986d28986008ff04d8c785fcbfe /usr.sbin/pmcstat | |
| parent | 1c6f6511c894b7650e784d2a2d97948f99898610 (diff) | |
| download | FreeBSD-src-0e1c93d3c1a464c1bcbd9ba493241df58a7d10ad.zip FreeBSD-src-0e1c93d3c1a464c1bcbd9ba493241df58a7d10ad.tar.gz | |
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%.
Diffstat (limited to 'usr.sbin/pmcstat')
| -rw-r--r-- | usr.sbin/pmcstat/pmcstat_log.c | 6 |
1 files changed, 3 insertions, 3 deletions
diff --git a/usr.sbin/pmcstat/pmcstat_log.c b/usr.sbin/pmcstat/pmcstat_log.c index f0e4939..40de320 100644 --- a/usr.sbin/pmcstat/pmcstat_log.c +++ b/usr.sbin/pmcstat/pmcstat_log.c @@ -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); } |
