On Fri, Jun 08, 2001 at 10:45:54AM -0400, Bill Sommerfeld wrote:
> The following is with -current..
> 
> 1) ubc needs many vnodes to effectively use physmem for vnode page
> cache.  For the NetBSD source tree, you need roughly 67000 vnodes to
> cache roughly 670k of data.
> 
> A 2G system autoconfigures with roughly 40000 vnodes, where the above
> ratio suggests that somewhere around 200000 vnodes might be a more
> appropriate size.

yes, we definitely need to adjust the tuning curves for various resources.
I've been increasing the number of vnodes via /etc/sysctl.conf on my machines
for a while now, but it would be nice to get more reasonable settings
by default.


> 2) atime updates throttle hot-cache read performance:
> 
> (this is after boosting kern.maxvnodes to 80000, followed by several
> "tar cvf /dev/null /usr/src" runs to get all of /usr/src into UBC
> cache)
> 
> # mount -u -o noatime /usr
> # tar cf /dev/null /usr/src
> tar: Removing leading / from absolute path names in the archive.
> # time tar cf /dev/null /usr/src 
> tar: Removing leading / from absolute path names in the archive.
> tar cf /dev/null /usr/src  0.67s user 9.79s system 99% cpu 10.525 total
> # mount -u -o atime /usr 
> # time tar cf /dev/null /usr/src
> tar: Removing leading / from absolute path names in the archive.
> tar cf /dev/null /usr/src  0.73s user 11.60s system 17% cpu 1:09.91 total
> # mount -u -o noatime /usr        
> # time tar cf /dev/null /usr/src
> tar: Removing leading / from absolute path names in the archive.
> tar cf /dev/null /usr/src  0.73s user 10.31s system 51% cpu 21.363 total
> # time tar cf /dev/null /usr/src
> tar: Removing leading / from absolute path names in the archive.
> tar cf /dev/null /usr/src  0.78s user 9.65s system 99% cpu 10.528 total


ok, any idea why updating atimes causes us to wait for i/o?

-Chuck