Re: [ANNOUNCE] Linux 2.6 Real Time Kernel

[Lee Revell <rlrevell@joe-job.com>]

On Sat, 2004-10-09 at 16:20, Robert Love wrote:
> On Sat, 2004-10-09 at 15:47 -0400, Lee Revell wrote:
> 
> > Yes.  The upper bound on the response time of an RT task is a function
> > of the longest non-preemptible code path in the kernel.  Currently this
> > is the processing of a single packet by netif_receive_skb.
> > 
> > AIUI hard realtime is about bounded response times.  How does this not
> > qualify?
> 
> I am actually in agreement with you, favoring this soft real-time
> approach, but this is not bounded response time or determinism.  There
> are no guarantees, no measurements conducted with all possible inputs,
> sizes, errors, and so on.  This soft real-time approach gives great
> average case--but the worst case is only a measurement on a specific
> machine in a specific workload.

I did not mean to say that VP approach alone can do hard realtime, that
was just an example.  But, when combined the MontaVista approach of
turning all but ~20 spinlocks into mutexes, it seems like the amount of
non-preemptible code is small enough that you could analyze it all and
start to make hard RT guarantees.

Lee