Re: Latest vfs scalability patch

Nick Piggin
2009-10-15T10:40:38Z

Hi Anton,

On Thu, Oct 15, 2009 at 09:08:54PM +1100, Anton Blanchard wrote:
>
> Hi Nick,
>
> > Several people have been interested to test my vfs patches, so rather
> > than resend patches I have uploaded a rollup against Linus's current
> > head.
> >
> > ftp://ftp.kernel.org/pub/linux/kernel/people/npiggin/patches/fs-scale/
> >
> > I have used ext2,ext3,autofs4,nfs as well as in-memory filesystems
> > OK (although this doesn't mean there are no bugs!). Otherwise, if your
> > filesystem compiles, then there is a reasonable chance of it working,
> > or ask me and I can try updating it for the new locking.
> >
> > I would be interested in seeing any numbers people might come up with,
> > including single-threaded performance.
>
> Thanks for doing a rollup patch, it made it easy to test. I gave it a spin on
> a 64 core (128 thread) POWER5+ box. I started simple by looking at open/close
> performance, eg:
>
> void testcase(void)
> {
> char tmpfile[] = "/tmp/testfile.XXXXXX";
>
> mkstemp(tmpfile);
>
> while (1) {
> int fd = open(tmpfile, O_RDWR);
> close(fd);
> }
> }
>
> At first the results were 10x slower. I took a look and it appears the
> MNT_MOUNTED flag is getting cleared by a remount (I'm testing on the root
> filesystem). This fixed it:

Oh dear, thanks for that. That bugfix is needed for the patchset
I just sent to be merged.

> --- fs/namespace.c~ 2009-10-15 04:34:02.000000000 -0500
> +++ fs/namespace.c 2009-10-15 04:35:00.000000000 -0500
> @@ -1711,7 +1711,8 @@ static int do_remount(struct path *path,
> else
> err = do_remount_sb(sb, flags, data, 0);
> if (!err)
> - path->mnt->mnt_flags = mnt_flags;
> + path->mnt->mnt_flags = mnt_flags |
> + (path->mnt->mnt_flags & MNT_MOUNTED);
> up_write(&sb->s_umount);
> if (!err) {
> security_sb_post_remount(path->mnt, flags, data);
>
> Attached is a before and after graph. Single thread performance is 20%
> faster, and we go from hitting a wall at 2 cores to scaling all the way
> to 64 cores. Nice work!!!

Nice looking graph, thanks! Did you use the rcu patch there as
well? (my open-close testing chokes RCU but your system might
be managing to keep outstanding callbacks below the threshold)