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SubjectRe: Strange performance change 59 -> 61/62
"Martin J. Bligh" <mbligh@aracnet.com> wrote:
>
> >> Some more stats ... which look rather suspicious. 600% increase for
> >> dentry_open and __mark_inode_dirty? Hmmmmm.
> >
> > __mark_inode_dirty() just got itself an smp_mb(). Would be instructive to
> > disable that.
> >
> > dentry_open(): don't know - fs/open.c hasn't changed at all. Perhaps
> > dcache_rcu has caused additional pingpong?
>
> 2.5.59-mjb6 84 __mark_inode_dirty
> 2.5.61-mjb1 594 __mark_inode_dirty
> 2.5.61-mjb1-no_mb 74 __mark_inode_dirty
>
> Yup, that fixed that one ... but presumably it was put there for a reason,
> so I can't just rip it out ;-) Thanks, I'll go take a closer look at the
> others.

mark_inode_dirty() tends to be called _very_ frequently. Too frequently.

Could you try remounting all filesystems noatime with

mount /mnt/point -o remount,noatime

and the below patch will prevent us calling the barrier-happy
current_kernel_time() for noatime mounts.


diff -puN fs/inode.c~update_atime-speedup fs/inode.c
--- 25/fs/inode.c~update_atime-speedup Fri Feb 21 12:17:00 2003
+++ 25-akpm/fs/inode.c Fri Feb 21 12:17:33 2003
@@ -1091,17 +1091,20 @@ sector_t bmap(struct inode * inode, sect

void update_atime(struct inode *inode)
{
- struct timespec now = CURRENT_TIME;
+ struct timespec now;

- /* Can later do this more lazily with a per superblock interval */
- if (timespec_equal(&inode->i_atime, &now))
- return;
if (IS_NOATIME(inode))
return;
if (IS_NODIRATIME(inode) && S_ISDIR(inode->i_mode))
return;
if (IS_RDONLY(inode))
return;
+
+ now = CURRENT_TIME;
+
+ /* Can later do this more lazily with a per superblock interval */
+ if (timespec_equal(&inode->i_atime, &now))
+ return;
inode->i_atime = now;
mark_inode_dirty_sync(inode);
}
_

-
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