Re: [patch] Real-Time Preemption, -RT-2.6.10-rc2-mm3-V0.7.32-6

From: Steven Rostedt
Date: Thu Dec 09 2004 - 08:37:31 EST

On Thu, 2004-12-09 at 10:32 +0100, Ingo Molnar wrote:
> * Steven Rostedt <rostedt@xxxxxxxxxxx> wrote:
> > Ingo really scares me with all the removing of local_irq_disables in
> > the rt mode. I'm not sure exactly what is going on there, and why they
> > can, or should be removed. Ingo?
> it is done so that the SLAB code can be fully preempted too. The SLAB
> code is of central importance to the -RT project, if it's not fully
> preemptible then that has a ripple effect on other subsystems (timer,
> signal code, file handling, etc.).
> So while making it fully preemptible was quite challenging (==dangerous,
> scary), i couldnt just keep the SLAB using raw spinlocks, due to the
> locking dependencies. (nor did i have any true inner desire to keep it
> non-preemptible - the point of PREEMPT_RT is to have everything
> preemptible. I want to see how much preemption the Linux kernel can take
> =B-) It has held up surprisingly well i have to say.)


> Ingo


Thanks for the write up. It really clears things up for me. Now I
understand your approach, not only for slabs, but other areas of the
kernel. Once again, thanks for the explanation.

-- Steve

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