Re: Nick's vfs-scalability patches ported to 2.6.33-rt

[Nick Piggin <npiggin@suse.de>]

On Thu, Feb 25, 2010 at 09:53:28PM -0800, john stultz wrote:
> Hey Thomas, Nick,
> 	I just wanted to let you know I've just finished forward porting Nick's
> patches to 2.6.33-rc8-rt2.  Luckily my forward port of Nick's patches to
> 2.6.33 applies on top of the -rt tree without any collisions, and I've
> added a handful of maybe sketchy fixups to get it working with -rt.
> 
> You can find the patchset here:
> http://sr71.net/~jstultz/dbench-scalability/patches/2.6.33-rc8-rt2/vfs-scale.33-rt.tar.bz2
> 
> Here's a chart showing how much these patches help dbench numbers on
> ramfs:
> http://sr71.net/~jstultz/dbench-scalability/graphs/2.6.33/ramfs-dbench.png
> 
> I've not done any serious stress testing with the patchset yet, but
> wanted to post it for your review.
> 
> Nick: I'd appreciate any feedback as to if any of my forward porting has
> gone awry. I'm still very green with respect to the vfs, so I don't
> doubt there are some issues hiding here.

BTW there are a few issues Al pointed out. We have to synchronize RCU
after unregistering a filesystem so d_ops/i_ops doesn't go away, and
mntput can sleep so we can't do it under RCU read lock.

The store-free path walk patches don't really have the required RCU
barriers in them either (which is fine for x86, but would have to be
fixed).