Re: static scheduling - SCHED_IDLE?

[Philipp Rumpf]

On Fri, Mar 09, 2001 at 09:09:13PM +0100, Jamie Lokier wrote:
> Rik van Riel wrote:
> > > Just raise the priority whenever the task's in kernel mode.  Problem
> > > solved.
> > 
> > Remember that a task schedules itself out at the timer interrupt,
> > in kernel/sched.c::schedule() ... which is kernel mode ;)
> 
> Even nicer.  On x86 change this:
> 
> reschedule:
> 	call SYMBOL_NAME(schedule)    # test
> 	jmp ret_from_sys_call
> 
> to this:
> 
> reschedule:
> 	orl $PF_HONOUR_LOW_PRIORITY,flags(%ebx)	
> 	call SYMBOL_NAME(schedule)    # test
> 	andl $~PF_HONOUR_LOW_PRIORITY,flags(%ebx)
> 	jmp ret_from_sys_call
> 
> (You get the idea; this isn't the best implementation).

A few months ago, I implemented preemptible kernel threads (locally;  I
tend to think the other patches are superior).  Part of the changes was
to separate schedule into __schedule() (common part), schedule_user()
(automatic schedule from entry.S) and schedule() (manual schedule in
kernel space);  besides making what Jamie proposed easier, we can also
save a few cycles in the (common) schedule_user case:

 - we never release the kernel lock
 - we can pass current to schedule_user
 - we just handled softirqs

this is 2.5 material though ...