top: just a small tweak to that history hash algorithm

This patch just raises the size of the hash table used
to calculate elapsed task stuff. The net result should
be less need for 'chaining' under pid hash collisions.

[ the hash scheme is intentionally kept as primitive ]
[ and, therefore, as fast as possible. it employs an ]
[ 'and' approach versus a 'mod' operation since both ]
[ yield similar distribution but the former approach ]
[ was 4 fewer cpu instructions in terms of overhead. ]

[ additionally, for hash collisions, 'chaining' uses ]
[ an array index rather than the usual pointer since ]
[ the HST_t guys may move when they are reallocated. ]

Signed-off-by: Jim Warner <james.warner@comcast.net>

diff --git a/top/top.c b/top/top.c
index 2afe648d95e31bd94c98d1efd0d663a8e027df7a..75ffe60b23ff720598395592166ca45cbb6bd195 100644 (file)
--- a/top/top.c
+++ b/top/top.c
@@ -190,7 +190,7 @@ static int    HHist_siz;               // max number of HST_t structs
 static HST_t *PHist_sav,               // alternating 'old/new' HST_t anchors
              *PHist_new;
 #ifndef OFF_HST_HASH
-#define       HHASH_SIZ  1024
+#define       HHASH_SIZ  4096
 static int    HHash_one [HHASH_SIZ],   // actual hash tables ( hereafter known
               HHash_two [HHASH_SIZ],   // as PHash_sav/PHash_new )
               HHash_nul [HHASH_SIZ];   // 'empty' hash table image