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From: tytso@mit.edu
To: Larry McVoy <lm@mcvoy.com>
Cc: tuhs@tuhs.org
Subject: Re: [TUHS] A/UX [was Linux is on-topic]
Date: Tue, 21 Jul 2020 23:13:13 -0400	[thread overview]
Message-ID: <20200722031313.GC1536749@mit.edu> (raw)
In-Reply-To: <20200721010411.GS26294@mcvoy.com>

On Mon, Jul 20, 2020 at 06:04:11PM -0700, Larry McVoy wrote:
> On Mon, Jul 20, 2020 at 05:11:48PM -0500, Ed Carp wrote:
> > On 7/20/20, Larry McVoy <lm@mcvoy.com> wrote:
> > 
> > > Clem should pay attention, in my opinion, this is how you do Unix and
> > > real time.  Because Unix is time sharing and throughput, that is the
> > > opposite of what real time is.  Wedging real time into Unix is a mistake.
> > 
> > Agreed.
> 
> So many people get this wrong, they want to make "real time" in Unix "good
> enough" and it messes with everything.  Victor's idea was awesome.
> 
> And you know what sucks?  I was on the Usenix review committee and I gave
> it 2 thumbs up but someone else, looking at you, Rob, said it was not 
> interesting because the real time kernel wasn't POSIX.  Even though the
> real time kernel had pipes, signals, and shared memory with Linux.
> 
> He was a bigger deal than me so it didn't get published.
> 
> I love the Rob in question, not Pike, but this was one of the most bone
> headed calls I've ever seen him make.  The world needed to see this.

Never fear, Victor's work got published in a number of Linux
conference, so it wasn't totally buried.

> Wind River bought it and buried it because it competed with their stuff
> that was nowhere near as good.

I can't get into the mind of Wind River. but having worked on a
commercial real-time extension to Linux, and having gotten a IBM
Systems Journal publication[1] out of it, I have a slightly different
perspective.

[1] https://ieeexplore.ieee.org/document/5386551

The issue is that there aren't that many good real-time programmers
Tavailable.  Furthermore, many real-time applications need to do a lot
more than data acquisition, so having access to POSIX API's in the
real time task is very attractive.  Sure, you can try to interchange
information between the real-time task and the POSIX task, but that's
a lot more complicated, and that's where the "not enough real-time
programmers" rears its head again.

This is even worse if you are working in a military application, since
small population of "can program real-time programmers" is further
reduced by "can get a security clearance".

Fortunately, with modern, fast CPU's, it's possible to do real-time
via brute force, and as it turns out, there are a very large number ofJ
real-time tasks which can deal with real-time latency that are tens of
milliseconds, at which point you even use real-time Java with a
real-time garbage collector running on a real-time Linux.  And that's
what Raytheon and the US Navy chose to use on their Zumwalt Class
destroyers, and that's how I and my team got the IBM Systems Journal
publication.   :-)

Sure, there will be some number of real-time task which needs
single-digit millisecond real-time guarantees --- in which case you
can write it in C using Real-time Linux.  And for those really cases
where you need latencies which are in the tens of microsecnds; then
yeah, at that point you might need specialized OS's.  But the cases
where you need fast, hard real-time is pretty rare compared to those
cases where real-time Java is sufficient.

Cheers,

					- Ted

  reply	other threads:[~2020-07-22  3:14 UTC|newest]

Thread overview: 106+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-07-17 18:08 [TUHS] H.J. Lu Bootable Root & Base System disks Norman Wilson
2020-07-17 18:14 ` John Cowan
2020-07-17 18:19 ` Larry McVoy
2020-07-17 19:53 ` [TUHS] Linux is on-topic Warren Toomey
2020-07-17 19:57   ` Larry McVoy
2020-07-17 20:00     ` Adam Thornton
2020-07-17 20:04       ` Larry McVoy
2020-07-17 20:03     ` Dan Cross
2020-07-17 23:31       ` A. P. Garcia
2020-07-19 10:26       ` emanuel stiebler
2020-07-17 20:07     ` Warren Toomey
2020-07-17 20:12       ` Warner Losh
2020-07-17 20:19       ` Clem Cole
2020-07-19  9:54       ` Sergio Pedraja
2020-07-17 20:08     ` Michael Kjörling
2020-07-17 20:55       ` Grant Taylor via TUHS
2020-07-17 21:28         ` Michael Kjörling
2020-07-18 20:22           ` Ed Carp
2020-07-18 20:29             ` Warner Losh
2020-07-19  2:31               ` Gregg Levine
2020-07-19  3:46               ` Wesley Parish
2020-07-19  4:42                 ` Grant Taylor via TUHS
2020-07-19 18:01                   ` Michael Parson
2020-07-20  8:47                     ` [TUHS] A/UX [was Linux is on-topic] arnold
2020-07-20  9:46                       ` Arno Griffioen
2020-07-20 16:35                         ` Arthur Krewat
2020-07-20 17:44                           ` Arno Griffioen
2020-07-20 19:07                         ` Rich Morin
2020-07-20 19:45                           ` Al Kossow
2020-07-20 19:49                             ` Al Kossow
2020-07-24  0:01                               ` Chris Hanson
2020-07-20 20:20                         ` Ed Carp
2020-07-20 21:02                           ` John Cowan
2020-07-20 22:27                             ` Ed Carp
2020-07-24  0:04                             ` Chris Hanson
2020-07-31 23:02                             ` Dave Horsfall
2020-07-31 23:12                               ` Richard Salz
2020-08-01  1:36                                 ` Larry McVoy
2020-08-01 16:08                                   ` Nemo Nusquam
2020-08-01 17:01                                     ` Arthur Krewat
2020-08-13  0:00                                   ` Dave Horsfall
2020-08-13  1:47                                     ` Larry McVoy
2020-08-13  3:15                                       ` Grant Taylor via TUHS
2020-08-13  4:02                                         ` Larry Cashdollar via TUHS
2020-08-31 21:12                                         ` Dave Horsfall
2020-09-03 14:10                                           ` Michael Parson
2020-08-13  1:53                                     ` Nemo Nusquam
2020-08-13 17:14                                   ` Dan Cross
2020-08-13 17:19                                     ` Henry Bent
2020-08-13 17:58                                       ` Warner Losh
2020-08-13 20:04                                       ` John Cowan
2020-08-13 20:52                                         ` Dan Cross
2020-08-14 17:31                                         ` Paul Winalski
2020-08-15  1:24                                           ` Dave Horsfall
2020-08-18 13:57                                         ` Derek Fawcus
2020-08-18 14:11                                           ` John Cowan
2020-08-31 21:20                                         ` Dave Horsfall
2020-08-13 19:18                                     ` Adam Thornton
2020-08-13 19:28                                       ` Warner Losh
2020-08-13 20:15                                         ` [TUHS] AIX link repost [was " Charles H Sauer
2020-08-13 20:09                                       ` [TUHS] " Rich
2020-08-13 20:16                                         ` Larry McVoy
2020-08-13 20:17                                         ` Dr Iain Maoileoin
2020-08-14  1:04                                         ` Christopher Browne
2020-08-14 17:18                                           ` Jim Capp
2020-08-14 17:37                                             ` Jim Capp
2020-08-14 17:39                                             ` Jon Steinhart
2020-08-15  0:33                                               ` Rich
2020-08-15  1:20                                                 ` Larry McVoy
2020-08-15  2:08                                                   ` Dave Horsfall
2020-08-15  2:47                                                     ` Warner Losh
2020-08-15 17:44                                                     ` Paul Winalski
2020-08-15 12:05                                                   ` Thomas Paulsen
2020-08-15  1:33                                                 ` Jon Steinhart
2020-08-15  2:02                                                 ` Dave Horsfall
2020-08-15  2:45                                                   ` Andrew Hume
2020-08-15 16:55                                                     ` William Cheswick
2020-08-15  3:29                                                   ` Larry McVoy
2020-08-15  1:40                                             ` Gregg Levine
2020-08-13 22:24                                     ` Grant Taylor via TUHS
2020-07-24  0:02                           ` Chris Hanson
2020-07-20  9:48                       ` Andrew Warkentin
2020-07-20 11:49                         ` Larry McVoy
2020-07-20 14:36                           ` Clem Cole
2020-07-20 17:24                           ` John Cowan
2020-07-20 22:11                           ` Ed Carp
2020-07-21  1:04                             ` Larry McVoy
2020-07-22  3:13                               ` tytso [this message]
2020-07-22  5:40                                 ` Bakul Shah
2020-07-22 14:16                                   ` Larry McVoy
2020-07-20 12:32                       ` Derrik Walker v2.0
2020-07-20 12:54                         ` Andrew Warkentin
2020-07-21  1:50                           ` Larry McVoy
2020-07-21  2:30                             ` Gregg Levine
2020-07-22  3:44                         ` Jason
2020-07-22 12:23                           ` Derrik Walker v2.0
2020-07-20 14:28                       ` Clem Cole
2020-07-22  3:50                         ` Jason
2020-07-22  4:26                           ` Henry Bent
2020-07-24  0:10                             ` Chris Hanson
2020-07-20  0:24               ` [TUHS] Linux is on-topic Ed Carp
2020-07-22  3:41             ` Jason
2020-07-22 16:15               ` Michael Parson
2020-07-18  3:34     ` Tomasz Rola
2020-07-18 16:45     ` Christopher Browne
2020-07-19  7:32       ` Lars Brinkhoff

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