Re: [PATCH] 2.5: conditional schedules with a preemptive kernel

[Robert Love]

On Thu, 2002-02-21 at 15:29, Linus Torvalds wrote:
> 
> On 20 Feb 2002, Robert Love wrote:
> > 
> > With a preemptive kernel, explicit conditional schedules when
> > preempt_count is zero are a waste of cycles and code size.
> 
> Hmm.. Are there any other kind?
> 
> Another way of saying this: how can a conditional schedule _ever_ be 
> nothing but a waste of cycles and code size with preemption enabled?
> 
> If the reason is the BKL, then I would much prefer those paths to be 
> BKL-fixed, than have two different conditional schedules.
> 
> In short, I'd rather get a patch that just unconditionally makes the 
> conditional schedules no-ops with preemption enabled. That would seem to 
> make a lot more sense.

I assume (and hope) the reason is always the BKL.

I would rather not eliminate any explicit reschedules from the kernel
for the preemptive kernel case only.  That sort of defeats a purpose
(response improvement) of the kernel.

And I wholeheartedly agree that the situations where the BKL is held
should be handled and an ideal solution is to just not explicitly
schedule anywhere in the kernel with a preemptive kernel.  But I suspect
this will involve a lot of dark magic wrt BKL locking semantics.

What do you have in mind?

	Robert Love