Subject: Re: RT patch acceptance
From: Steven Rostedt <rostedt@goodmis.org>
To: Lee Revell <rlrevell@joe-job.com>
Cc: Andrea Arcangeli <andrea@suse.de>, Esben Nielsen <simlo@phys.au.dk>,
       linux-kernel@vger.kernel.org, akpm@osdl.org, hch@infradead.org,
       dwalker@mvista.com, Ingo Molnar <mingo@elte.hu>,
       Sven-Thorsten Dietrich <sdietrich@mvista.com>, Andi Kleen <ak@muc.de>,
       "Bill Huey (hui)" <bhuey@lnxw.com>,
       Nick Piggin <nickpiggin@yahoo.com.au>,
       James Bruce <bruce@andrew.cmu.edu>
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Organization: Kihon Technologies
Date: Tue, 31 May 2005 19:41:27 -0400
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On Tue, 2005-05-31 at 17:47 -0400, Lee Revell wrote:
> On Tue, 2005-05-31 at 17:22 -0400, Steven Rostedt wrote:
> > I wouldn't call RTAI, RTLinux or a nano-kernel (embedded with Linux)
> > "Diamond" hard.  Maybe "Ruby" hard, but not diamond.  Remember, I use to
> > test code that was running airplane engines, and none of those mentioned
> > would qualify to run that.
> 
> I think trying to make these types of distinctions is a waste of time.
> What matters is the MTBF of the software relative to the hardware on a
> given system.  It would be stupid to use a commercial RTOS for a cell
> phone because they fall apart in a year anyway and users don't seem to
> care.  Ditto anything running on PC hardware.  For an airplane the MTBF
> obviously must be more in line with that hardware which hopefully is way
> more reliable.

Agreed.  I only brought up the stupid names just to show that there's
not a black and white aspect to what RT is.  It's mainly a black art
since there's no way to know how many bugs a program has, and how do you
truly calculate the MTBF, other than running it on the hardware itself?

> Only the engineer who designs the system knows for sure, so if the RT
> app people say PREEMPT_RT is good enough for a *very* large set of the
> applications that they currently need a commercial RTOS for, they should
> be given the benefit of the doubt.  To say otherwise is to assert that
> you know their hardware (be it desktop PC, digital audio workstation, or
> airplane) better than they do.

True, but do they really know how good PREEMPT_RT is, compared to those
that develop it and the kernel?  But I'm fighting to get PREEMPT_RT into
the kernel, since I really think it would be used by quite a lot in the
industry.  Just not the normal Desktop user.

-- Steve


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