Google SoC 2009 Idea
kientzle at freebsd.org
Thu Feb 26 09:19:37 PST 2009
Robert Watson wrote:
> On Wed, 25 Feb 2009, Tim Kientzle wrote:
>>> I have not gone through the process scheduler code of Free BSD.
>>> Hence, I am not yet aware about the current support for Multicore
>> Since you posted to a lot of different lists, I think you probably
>> don't already use FreeBSD. (If you did, why would you post to NetBSD
>> and DragonflyBSD lists?) Scheduler work is quite complex and
>> interacts heavily with the rest of the system; it may not be a good
>> choice for someone who doesn't already have a lot of experience with
> All the things you say are true, but let's not be too hard on the new
> guy, however -- many of our GSoC students don't have previous FreeBSD
> kernel-hacking experience. However, it does mean that they have to pick
> project ideas that are well-suited to a significant warmup and
> investigation period on the front end of the project.
I apologize to Siddharth and others if I came off overly
harsh. My intention was to caution him that he should
plan for a lot of work prior to GSoC if he wants to
tackle something that's at the core of the OS like this.
> I'm also not convinced that a scheduler project along these lines would
> be the most successful, but I wonder if a more experimental-spin
> proposal for looking at how to investigate poor scheduling decisions
> using dtrace, instrumentation and metrics to help us understand
> performance on NUMA systems, and exploring the impact of heuristics
> might go a long way.
That's a good idea. The thing that's always impressed
me about scheduling work is how very difficult it is to
test. It's easy to change the scheduler code; it's
much harder to measure whether those changes have
made the scheduler better or not.
Some testing support would help. Ideally, something
non-intrusive that could be easily run on a lot
of different machines so as to collect better information
about the impacts of scheduler changes:
* Load balancing: How effectively are all cores being used?
* CPU switching: What percentage of the time does a thread
stay on the same core?
* NUMA statistics: How often does a thread get scheduled on a
different processor from it's allocated memory?
* Priority inversion: How often is a higher-priority thread
idle while a lower-priority thread is running?
A student who built such a tool and then ran some tests
with a variety of hardware and workloads could really
do a lot to advance scheduler development. Eventually,
turning such a tool into something that anyone could run
and upload data to a central collection site could be
a huge advance.
Certainly something to think about...
More information about the freebsd-hackers