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| author | emaste <emaste@FreeBSD.org> | 2014-05-23 17:46:00 +0000 |
|---|---|---|
| committer | emaste <emaste@FreeBSD.org> | 2014-05-23 17:46:00 +0000 |
| commit | e7613520673b6f7fb6b5b77f7c9ac3b31982f6ae (patch) | |
| tree | c7a21d5b2af4d4b6e5afe344d322a3680e62de28 /usr.sbin/pmcstat | |
| parent | 80044281eb7ca569563950bc5c86bcd1a4d9c7c6 (diff) | |
| download | FreeBSD-src-e7613520673b6f7fb6b5b77f7c9ac3b31982f6ae.zip FreeBSD-src-e7613520673b6f7fb6b5b77f7c9ac3b31982f6ae.tar.gz | |
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%.
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); } |
