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

Casey Ransberger casey.obrien.r at gmail.com
Fri Apr 19 07:38:06 UTC 2013

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? ;)

Basically it would be a fork, done with the original author's blessing.
This would also make it easy to change the (rather unfortunate) f-ing name
of the thing.

For the curious, at the end of this message I'm linking to a bit about why
he wrote it. It's worth mentioning that it's rather in the spirit of
simple-is-better, which I think fits with the Squeak ethos a little. Not to
mention that it's aimed at the desktop/personal computing experience,
rather than CFS's focus on big iron and tons of CPUs, so it's really
appropriate to the Raspberry Pi, as well as potentially the XO.

The only real advantage to forking the work is to bring support for it into
the Squeak community. I doubt I'll have any more luck lobbying the kernel
crowd to get it in as a secondary process scheduler than Con did, but
maybe, just maybe, the Raspbian folks will see some value in making the
Squeak VM go faster / possibly use less power (given that they're putting
Scratch on the desktop by default) and be open to taking the patch.
Especially if I can come with benchmarks that make it desirable across the
board on the device (it sounds like it can probably bring the rain on that
count if I'm reading this stuff right.)

Whether or not I get warm feelings from the Raspbian folks, I'm going to
look at "how can I make this patch as painless as possible to apply to as
many distros as possible?"

Of course if I actually do this, I can probably kiss my social life
goodbye, so I'm not without reservations. Not to mention that the number of
people who'll care is probably smaller than one might hope.

I wondered what folks on vm-dev might think. If this is another one of my
crazy projects that no one actually wants, please let me know posthaste :D


If you're worried that I might not be qualified to maintain a kernel patch,
I think this should help to assuage your fears:


And here's Con's rationale for implementing it. Warning: you might not want
to pull this up while your parents are watching unless you've had a good
long talk with them about what words are appropriate to use in various
social contexts. Raising parents can be very challenging! And putting soap
in their mouths only seems to upset them...


Casey Ransberger
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