svn commit: r211126 - head/sys/kern

[Ivan Voras]

Author: ivoras
Date: Mon Aug  9 22:56:10 2010
New Revision: 211126
URL: http://svn.freebsd.org/changeset/base/211126

Log:
  Bumping the read-ahead count once more, to value equivalent to 512 KiB on
  most system, based on benchmark results on a low-end fibre channel SAN
  under VMWare:
  
  vfs.read_max		read performance
  8  (historical default)	83 MB/s
  16 (recent bump)	131 MB/s
  32 (this version)	152 MB/s
  64			157 MB/s
  
  (results are +/- 3 MB/s)
  
  As read-ahead is heuristic, based on past IO requests, it shouldn't be
  problematic. The new default is still smaller then in other OSes.

Modified:
  head/sys/kern/vfs_cluster.c

Modified: head/sys/kern/vfs_cluster.c
==============================================================================
--- head/sys/kern/vfs_cluster.c	Mon Aug  9 22:30:14 2010	(r211125)
+++ head/sys/kern/vfs_cluster.c	Mon Aug  9 22:56:10 2010	(r211126)
@@ -71,7 +71,7 @@ static int write_behind = 1;
 SYSCTL_INT(_vfs, OID_AUTO, write_behind, CTLFLAG_RW, &write_behind, 0,
     "Cluster write-behind; 0: disable, 1: enable, 2: backed off");
 
-static int read_max = 16;
+static int read_max = 32;
 SYSCTL_INT(_vfs, OID_AUTO, read_max, CTLFLAG_RW, &read_max, 0,
     "Cluster read-ahead max block count");