Re: [rfc][patch] store-free path walking

Nick Piggin
2009-10-09T10:44:38Z

On Thu, Oct 08, 2009 at 11:15:27PM -0700, David Miller wrote:
> From: Nick Piggin <npiggin@suse.de>
> Date: Fri, 9 Oct 2009 05:50:50 +0200
>
> > OK, I got rid of this guy from the RCU walk. Basically now hold
> > vfsmount_lock over the entire RCU path walk (which also pins the mnt)
> > and use a seqlock in the fs struct to get a consistent mnt,dentry
> > pair. This also simplifies the walk because we don't need the
> > complexity to avoid mntget/mntput (just do one final mntget on the
> > resulting mnt before dropping vfsmount_lock).
> >
> > vfsmount_lock adds one per-cpu atomic for the spinlock, and we
> > remove two thread-shared atomics for fs->lock so a net win for
> > both single threaded performance and thread-shared scalability.
> > Latency is no problem because we hold rcu_read_lock for the same
> > length of time anyway.
> >
> > The parallel git diff workload is improved by serveral percent.
>
> Sounds sweet Nick, can't wait to play with your next set of
> patches here.

Oh and the RCU patch there just in case you want to try some file
open/close benchmarks. Turns out I broke Paul's new scalable RCU ;)