Re: [patch] Real-Time Preemption, -RT-2.6.10-rc2-mm2-V0.7.29-0

[Florian Schmidt]

On Fri, 19 Nov 2004 22:22:42 -0500
Lee Revell <rlrevell@xxxxxxxxxxx> wrote:

> On Thu, 2004-11-18 at 17:46 +0100, Ingo Molnar wrote:
> > i have released the -V0.7.29-0 Real-Time Preemption patch, which can be
> > downloaded from the usual place:
> > 
> > 	http://redhat.com/~mingo/realtime-preempt/
> 
> I tried this with CONFIG_PREEMPT_VOLUNTARY (which should theoretically
> work like the earlier VP patches, right?) to test for regressions.  The
> boot process hung after initializing my IDE controller.

I thought so, too, until ingo set me straight (quote ingo):

here are the different layers of preemption:

 - !PREEMPT
 - PREEMPT_VOLUNTARY
 - PREEMPT
 - PREEMPT_RT

each step forward decreases latencies, at the cost of more runtime 
overhead.

so PREEMPT_VOLUNTARY is not "the" feature anymore, it's "a" feature down
the hierarchy. In fact the focus is mostly on PREEMPT_RT now.

quote end..

So with RP kernels, PREEMPT is what gives best latency when full realtime
preemption is not an option

flo
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