Re: scalability investigation: Where can I get your latest patches?

["Zhang, Yanmin" <yanmin_zhang@linux.intel.com>]

On Thu, 2010-08-05 at 21:44 +1000, Nick Piggin wrote:
> On Wed, Aug 04, 2010 at 09:04:03AM +0800, Zhang, Yanmin wrote:
> > We ran lots of benchmarks on many machines. Below is something to
> > share with you.
> > 
> > Improvement:
> > 1) We get about 30% improvement with kbuild workload on Nehalem
> > machines. It's hard to improve kbuild performance. Your tree does.
> > 
> > Issues:
> > 1) Compiling fails on a couple of file systems, such like CONFIG_ISO9660_FS=y.
> > 2) dbenchthreads has about 50% regression. We connect a JBOD of 12 disks to
> > a machine. Start 4 dbench threads per disk.  We run the workload under
> > a regular user account. If we run it under root account, we get 22%
> > improvement instead of regression.  The root cause is ACL checking.
> > With your patch, do_path_lookup firstly goes through rcu steps which
> > including a exec permission checking. With ACL, the __exec_permission
> > always fails. Then a later nameidata_drop_rcu often fails as
> > dentry->d_seq is changed.
> 
> Oh one other thing I wanted to ask about. d_seq changing should not
> be too common. If the directory is renamed, or if it is turned negative
> should be the only cases in which we should see a d_seq changes.
> 
> Or unless there is a bug and it is checking the wrong sequence or
> against the wrong dentry. 
Sorry for misleading you. It fails at the beginning in nameidata_drop_rcu
because (nd->flags & LOOKUP_FIRST) is true.

> How often would you say nameidata_drop_rcu
> fails (without the following acl rcu patches)?
I instrument kernel and find nameidata_drop_rcu always fails.