On Tue, Dec 20, 2011 at 10:07:22AM +0100, Francois Tigeot wrote:
> Most of the VFS accounting work is now in the tree (and disabled by
default,
> enable it with vfs.accounting_enabled="1" in /boot/loader.conf).
> Only a potentially disruptive commit to enable it for / has not been
pushed.
> 
> Since VFS accounting uses a per mount-point spinlock to protect its
counters, 
> there is some concern it will degrade write performance on SMP machines.
> 
> To measure if this was the case or not, I've run some blogbench
benchmarks on
> a small Xeon system; the details of the test and the results are in the
> attached PDF.
> 
> VFS accounting kernel was from 2011-12-19
> Kernel without VFS accounting was from 2011-11-19
> 
> For my part I think the results are inconclusive: either there's no
measurable
> performance difference or the choice of benchmark was bad.

I've made a plot which shows the results in more evident way (if I
correctly
understand the test results data).

-- 
Dmitrij D. Czarkoff