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

[Nick Piggin <npiggin@suse.de>]

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. How often would you say nameidata_drop_rcu
fails (without the following acl rcu patches)?