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| author | Ed Maste <emaste@FreeBSD.org> | 2014-05-16 03:05:53 +0000 |
|---|---|---|
| committer | Ed Maste <emaste@FreeBSD.org> | 2014-05-16 03:05:53 +0000 |
| commit | dc17b1feaa6bcac1f8c3f0aa5ad02ae00045c411 (patch) | |
| tree | 8489ff7f77613986d28986008ff04d8c785fcbfe /usr.sbin | |
| parent | 06e36338cab18d6856ee9f7d542d0e1421f095a1 (diff) | |
| download | src-dc17b1feaa6bcac1f8c3f0aa5ad02ae00045c411.tar.gz src-dc17b1feaa6bcac1f8c3f0aa5ad02ae00045c411.zip | |
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%.
Notes
Notes:
svn path=/head/; revision=266208
Diffstat (limited to 'usr.sbin')
| -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 f0e493959acb..40de320f17a1 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); } |