Subject: Re: RT patch acceptance
From: Lee Revell <rlrevell@joe-job.com>
To: James Bruce <bruce@andrew.cmu.edu>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>, "Bill Huey (hui)" <bhuey@lnxw.com>,
       Andi Kleen <ak@muc.de>, Sven-Thorsten Dietrich <sdietrich@mvista.com>,
       Ingo Molnar <mingo@elte.hu>, dwalker@mvista.com, hch@infradead.org,
       akpm@osdl.org, linux-kernel@vger.kernel.org
In-Reply-To: <429BA27A.5010406@andrew.cmu.edu>
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Date: Mon, 30 May 2005 22:06:44 -0400
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On Mon, 2005-05-30 at 19:32 -0400, James Bruce wrote:
> This is sort of confused 
> by the fact that Ingo called it "hard realtime" because he measured a 
> maximum latency during a stress test.  Unfortunately that's not
> really 
> hard realtime if you are just measuring it; Rather its "really damn
> good 
> soft realtime".  An analysis of code paths could be done to determine
> if 
> something really does satisfy hard-RT constraints, but to my
> knowledge 
> that's not on the table at this point.  So you're discussing soft 
> realtime if you're dicussing the RT patch.
> 
> So its really just a misunderstanding 

No, *you're* the one misunderstanding.

Since *everything* is preemptible except a few known code paths whose
execution times determine the maximum possible latency from interrupt to
running the highest priority user process.

That's the determinism, no more, no less.  But some people inexplicably
think this thread is about providing deterministic hard RT performance
for some subset of system calls, or disk IO or something, none of which
have anything to do with PREEMPT_RT.

Lee

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