[src/ad-namecache]: src/sys/sys Move nc_key up, so cache_lookup_entry() only ...

[ad <ad%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/a37174c42cec
branches:  ad-namecache
changeset: 983028:a37174c42cec
user:      ad <ad%NetBSD.org@localhost>
date:      Sat Mar 21 22:04:17 2020 +0000

description:
Move nc_key up, so cache_lookup_entry() only needs to touch one cache line
at each step.

diffstat:

 sys/sys/namei.src |  9 +++++----
 1 files changed, 5 insertions(+), 4 deletions(-)

diffs (37 lines):

diff -r 6880c61e0f7c -r a37174c42cec sys/sys/namei.src
--- a/sys/sys/namei.src Sat Mar 21 22:00:55 2020 +0000
+++ b/sys/sys/namei.src Sat Mar 21 22:04:17 2020 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: namei.src,v 1.47.2.7 2020/03/04 20:21:05 ad Exp $      */
+/*     $NetBSD: namei.src,v 1.47.2.8 2020/03/21 22:04:17 ad Exp $      */
 
 /*
  * Copyright (c) 1985, 1989, 1991, 1993
@@ -199,11 +199,12 @@
 #define        NCHNAMLEN       sizeof(((struct namecache *)NULL)->nc_name)
 
 /*
- * Namecache entry.  
+ * Namecache entry.
  *
  * This structure describes the elements in the cache of recent names looked
  * up by namei.  It's carefully sized to take up 128 bytes on _LP64, to make
- * good use of space and the CPU caches.
+ * good use of space and the CPU caches.  Items used during RB tree lookup
+ * (nc_tree, nc_key) are clustered at the start of the structure.
  *
  * Field markings and their corresponding locks:
  *
@@ -216,11 +217,11 @@
 struct nchnode;
 struct namecache {
        struct  rb_node nc_tree;        /* d  red-black tree, must be first */
+       int64_t nc_key;                 /* -  hash key */
        TAILQ_ENTRY(namecache) nc_list; /* v  vp's list of cache entries */
        TAILQ_ENTRY(namecache) nc_lru;  /* l  pseudo-lru chain */
        struct  vnode *nc_dvp;          /* -  vnode of parent of name */
        struct  vnode *nc_vp;           /* -  vnode the name refers to */
-       int64_t nc_key;                 /* -  hash key */
        int     nc_lrulist;             /* l  which LRU list its on */
        short   nc_nlen;                /* -  length of the name */
        char    nc_whiteout;            /* -  true if a whiteout */