unionfs makes -CURRENT very sluggish

[Jeremie Le Hen]

Hi,

On Tue, Apr 22, 2008 at 10:34:35PM +0200, Jeremie Le Hen wrote:
> I tried to compile lib/ncurses through unionfs.  It is utterly slow, no
> matter I mount with noatime or not.
> 
> Relevant mounts:
> % /usr/src on /space/chroot/usr/src (nullfs, local, read-only)
> % <above>:/space/chroot/usr/src.union on /space/chroot/usr/src (unionfs, local)
> 
> % root:~# chroot /space/chroot
> % root:/# cd /usr/src/
> % root:/# make buildenv
> % # cd lib/ncurses
> % # time make
> 
> Compile time without noatime:
>      5089.47 real      1670.72 user      3364.89 sys
> 
> Compile time with noatime:
>      5083.22 real      1664.10 user      3369.22 sys
> 
> Now if I remove the unionfs mount and just use nullfs:
>       255.47 real       150.51 user        83.82 sys
> 
> 
> As you can see, most of the time is spent in kernel.  I'm recompiling my
> kernel with hwpmc right now in order to profile it.  Any other debug
> hint would be welcome.
> 
> FWIW, "while sleep 1 ; do date ; done" runs jerkily when unionfs is run:
> Tue Apr 22 21:20:06 CEST 2008
> Tue Apr 22 21:20:13 CEST 2008
> Tue Apr 22 21:20:17 CEST 2008
> Tue Apr 22 21:20:22 CEST 2008
> Tue Apr 22 21:20:29 CEST 2008
> 
> Whereas it runs smoothly without unionfs.
> 
> I'll give the result of hwpmc ASAP.

I've upgraded to the latest -CURRENT and the problem went away.  Sorry
for the noise.

Regards,
-- 
Jeremie Le Hen
< jeremie at le-hen dot org >< ttz at chchile dot org >