[linuxdc-dev][PATCH] Preemptible Kernel for SH (and thus dreamcast)

[Robert L. <rm...@te...>]

I also want to mention that we have a version of the preemptible kernel
for the SH arch now, and it seems to run lovely on the Dreamcast.

It is available at:
	http://www.kernel.org/pub/linux/kernel/people/rml/sh/preempt-kernel-sh-2.4.16-1.patch

You will also need the base preempt-kernel patch at:
	http://www.kernel.org/pub/linux/kernel/people/rml/preempt-kernel/v2.4/preempt-kernel-rml-2.4.16-1.patch

And a recent SH tree. The "linux" module in CVS at
http://sf.net/projects/linuxsh was recently updated to 2.4.16. 
Alternatively, here is a patch to bring 2.4.16 in sync with the SH tree:
	http://www.kernel.org/pub/linux/kernel/people/rml/sh/sh-update-rml-2.4.16-1.patch

There is a bit of information about the preemptible kernel at
http://tech9.net/rml/linux as well as LWN, slashdot, etc.  Basically,
the current linux kernel does not allow processes to be preempted when
operating inside the kernel.  I.e., kernel calls run until completion --
this implies that even if task A needs to run, if task B is running and
in the kernel, task A won't be scheduled until task A is done.  The
degradation this causes to latency and system response is clear. 
Further, however, since with the preempt-kernel patch I/O-bound tasks
are scheduled as-soon-as I/O is available, throughput tends to increase,
too.  We are aiming at inclusion in 2.5.

Its pretty neat.  If nothing else, tell your friends you have a fully
preemptible Dreamcast.  Or something.

Comments and feedback is welcome,

	Robert Love