At 2006/6/6 09:46-0700  Mike Kravetz writes:

On Thu, Jun 01, 2006 at 03:12:15PM +1000, Christopher Yeoh wrote:

quoted

Here's a patch we've used for collecting hcall counts and times.

Thanks for the patch/code Chris!  I'm using this as a basis for something
that we may want to merge into the tree.  Just a couple of questions.

Your 'wrappers' have the following general form:


Can you explain the need for barrier(s) before and after the call to the
real routine?  It usually takes me a couple days of thought to figure out
exactly where these are needed. :)

Ah oops, it turns out I was wrong and they're not necessary after all.

The use of get_cpu_var/put_cpu_var result in disabling/enabling preemption.
I can understand why this would be desirable to assure the accuracy of the
statistics.  But, I was wondering if the desired accuracy is worth the added
overhead.  My thought was to make these as lightweight as possible and
sacrifice some accuracy if necessary.  After all, no 'internal decisions' are
being made because of this data.  It is simply exposed to user land.
Thoughts?

For what we were using them for at the time we weren't really
concerned about a small degradation in performance and were more
interested in accuracy. I guess I'd recommend doing some benchmarking
to see what difference they really make.

Chris
-- 
cyeoh@au.ibm.com
IBM OzLabs Linux Development Group
Canberra, Australia