[Vm-dev] BFS and CFS and Cogs, Oh My

Alex Bradbury asb at asbradbury.org
Fri Apr 19 13:16:13 UTC 2013

On 19 April 2013 08:38, Casey Ransberger <casey.obrien.r at gmail.com> wrote:
> I had a brief chat with Con Kolivas, who did BFS (which implements kernel stuff that will make Cog happier under Linux on machines with sub-supercomputing quantities of CPUs) tonight.
> It sounds like there are actually two reasons it hasn't made it into the mainline kernel:
> a) he doesn't have time to support it, and
> b) the other kernel folks don't want it.
> Oh well. Since right now I'm focused on Raspbian, I sent a message explaining what it was, why I want it, etc on their web board. If I do get it in, support would have to fall to me. Yikes, right? ;)

Yes, for political reasons it seems unlikely anything like BFS would
get in to the upstream kernel. If someone can do work to actually show
noticeable performance gains then that would make us (the Raspberry Pi
Foundation) interested in exploring further. Real workloads that
perform much better with an alternative scheduler would be much more
interesting than microbenchmarks. Of course the next step after that
wouldn't be dumping the upstream scheduler and switching to BFS, but
it would certainly justify taking a closer look.

I'm not entirely sure why you want to fork BFS - as far as I can see
Con Kolivas is keeping the BFS and his larger -ck patchset up to date
with upstream releases.

In conclusion (from a Raspberry Pi perspective): please do play with
BFS on the pi, do something useful with it (if it solves the recently
discussed issues with heartbeat+cogvm then swell), then let's think
about where to go from there.



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