From: Anton Blanchard <anton@samba.org>
Directory notify code was showing up in a dd bs=1024k from 2 raid arrays
on an emulex FC adapter:
3635 69.4896 vmlinux-2.6.5 .default_idle
332 6.3468 vmlinux-2.6.5 .__copy_tofrom_user
112 2.1411 vmlinux-2.6.5 .save_remaining_regs
76 1.4529 vmlinux-2.6.5 .scsi_dispatch_cmd
64 1.2235 vmlinux-2.6.5 .dnotify_parent
61 1.1661 vmlinux-2.6.5 .do_generic_mapping_read
We already have a sysctl to enable/disable it, the patch below uses it
in dnotify_parent. dnotify_parent disappears and idle time goes up:
4508 70.8582 vmlinux-2.6.5 .default_idle
253 3.9767 vmlinux-2.6.5 .__copy_tofrom_user
142 2.2320 vmlinux-2.6.5 .save_remaining_regs
88 1.3832 vmlinux-2.6.5 .shrink_zone
84 1.3203 vmlinux-2.6.5 .elx_drvr_unlock
75 1.1789 vmlinux-2.6.5 .scsi_dispatch_cmd
69 1.0846 vmlinux-2.6.5 .do_generic_mapping_read
Of course, to gain this small speedup isers need to know to set
/proc/sys/fs/dir-notify-enable to zero. Nobody does that.
---
25-akpm/fs/dnotify.c | 3 +++
1 files changed, 3 insertions(+)
diff -puN fs/dnotify.c~dnotify_parent-speedup fs/dnotify.c
--- 25/fs/dnotify.c~dnotify_parent-speedup 2004-04-09 18:30:07.434716160 -0700
+++ 25-akpm/fs/dnotify.c 2004-04-09 18:30:07.443714792 -0700
@@ -154,6 +154,9 @@ void dnotify_parent(struct dentry *dentr
{
struct dentry *parent;
+ if (!dir_notify_enable)
+ return;
+
spin_lock(&dentry->d_lock);
parent = dentry->d_parent;
if (parent->d_inode->i_dnotify_mask & event) {
_