Subject: Context switch revamp
To: None <firstname.lastname@example.org>
From: Gregory McGarry <email@example.com>
Date: 09/13/2002 08:33:39
I'm keen to separate the scheduler and the context switching
functionality. This is useful for the following reasons:
- simplifies the possibility of replacing the scheduler;
- aligns better with the scheduler activations changes;
- allows microtime optimisations if switching to self; and
- cleans up the horrendous cpu_switch() code.
To achieve this, I propose changing the following function:
* void cpu_switch(struct proc *curp, struct proc *newp)
* Switch from process curp to process newp. Scheduler
* lock must be held and interrupts disabled.
and the addition of the following functions:
* struct proc *chooseproc(void)
* Find a runnable process. Wait if necessary. Scheduler
* lock must be held.
* void cpu_idle(void)
* Idle. Scheduler lock must be held and interrupts
With these changes I have been able to make chooseproc() largely
machine independent and push it up into mi_switch(). The ultimate
goal would be to push it even higher out of mi_switch(). I have
kept chooseproc() as an assembler routine ATM.
These changes are easy to do piecemeal. So I suggest introducing
something like __HAVE_CHOOSEPROC to simplify a changeover for
I have done this successfully on i386 and mips. A first-go
proof-of-concept for i386 is available at:
Shouldn't take much to get the patch going. The i386 stuff still
needs a cleanup. In fact, I think the i386 code is overly aggressive
with interrupt blocking, but its not clear what the run queue
requirements are with respect to interrupt protection.
I'm looking for a "Let's do it, clean it up", or a "I don't think so".
-- Gregory McGarry <firstname.lastname@example.org>