Re: Engineering degree for embedded systems

Subject	Re: Engineering degree for embedded systems
Newsgroups	comp.arch.embedded
References	(8 earlier) <708a5706-d12f-6e8f-442d-44efeafb7cc9@electrooptical.net> <5C1iB.390268$gM6.248510@fx03.am4> <ombs5g$iva$1@dont-email.me> <PTeiB.707621$HS1.256337@fx12.am4> <ombvsd$ui3$1@dont-email.me>
From	Tom Gardner <spamjunk@blueyonder.co.uk>
Message-ID	<b5giB.179066$W97.95506@fx36.am4> (permalink)
Organization	virginmedia.com
Date	2017-08-08 11:09 +0100

Show all headers | View raw

On 08/08/17 10:26, David Brown wrote:
> On 08/08/17 10:46, Tom Gardner wrote:
>> On 08/08/17 09:23, David Brown wrote:
>>> On 07/08/17 19:40, Tom Gardner wrote:
>>>> On 07/08/17 17:36, Phil Hobbs wrote:
>>>
>>>>> My stuff is all pthreads, because std::thread didn't exist at the time,
>>>>> but it does now, so presumably Boehm's input has been taken into
>>>>> account.
>>>>
>>>> I'm told C/C++12 /finally/ has a memory model, so perhaps
>>>> that will (a few decades too late) ameliorate the problem.
>>>> We'll see, but I'm not holding my breath.
>>>
>>> You mean C11/C++11 ?
>>
>> Oh.... picky picky picky :)
>
> Well, if you decide to look this up on google, it should save you a bit
> of false starts.

Unfortunately google doesn't prevent idiots from making
tyupos :) (Or is that fortunately?)

>>> Whether people will use them
>>> appropriately or not, is another matter.
>>
>> My experience is that they won't. That's for two reasons:
>> 1) not really understanding threading/synchronisation
>> issues, because they are only touched upon in schools.
>> Obviously that problem is language agnostic.
>
> Agreed.  This stuff is hard to understand if you want to get correct
> /and/ optimally efficient.
>
>> 2) any subtleties in the C/C++ specification and
>> implementation "suboptimalities"; I expect those will
>> exist :(
>
> I have read through the specs and implementation information - quite a
> bit of work has gone into making it possible to write safe code that is
> more efficient than was previously possible (or at least practical).  It
> is not so relevant for small embedded systems, where you generally have
> a single core and little in the way of write buffers - there is not
> much, if anything, to be gained by replacing blunt full memory barriers
> with tuned load-acquire and store-release operations.  But for bigger
> systems with multiple cpus, a full barrier can cost hundreds of cycles.

Agreed, with the caveat that "small" ain't what it used to be.
Consider Zynqs: dual-core ARMs with caches and, obviously, FPGA
fabric.
Consider single 32 core MCUs for £25 one-off. (xCORE)
There are many other examples, and that trend will continue.


> There is one "suboptimality" - the "consume" memory order.  It's a bit
> weird, in that it is mainly relevant to the Alpha architecture, whose
> memory model is so weak that in "x = *p;" it can fetch the contents of
> *p before seeing the latest update of p.  Because the C11 and C++11
> specs are not clear enough on "consume", all implementations (AFAIK)
> bump this up to the stronger "acquire", which may be slightly slower on
> some architectures.

One of C/C++'s problems is deciding to cater for, um,
weird and obsolete architectures. I see /why/ they do
that, but on Mondays Wednesdays and Fridays I'd prefer
a concentration on doing common architectures simply
and well.



>> ISTR that in the early-mid naughties there was a triumphant
>> announcement of the first /complete/ C or C++ compiler - 5
>> or 6 years after the standard was published! Of course many
>> compilers had implemented a usable subset before that.
>>
>
> Things have changed a good deal since then.  The major C++ compilers
> (gcc, clang, MSVC) have complete C++11 and C++14 support, with gcc and
> clang basically complete on the C++17 final drafts.  gcc has "concepts",
> slated for C++20 pretty much "as is", and MSVC and clang have prototype
> "modules" which are also expected for C++20 (probably based on MSVC's
> slightly better version).
>
> <http://en.cppreference.com/w/cpp/compiler_support>
>
> These days a feature does not make it into the C or C++ standards unless
> there is a working implementation in at least one major toolchain to
> test it out in practice.

Yes, but I presume that was also the case in the naughties.
(I gave up following the detailed C/C++ shenanigans during the
interminable "cast away constness" philosophical discussions)

The point was about the first compiler that (belatedly)
correctly implemented /all/ the features.


>>> And people got some things right, and some things wrong, at that time.
>>> I think the same thing will apply now that they /have/ memory models.
>>
>> Agreed.
>>
>> I'm gobsmacked that it took C/C++ so long to get around to
>> that /fundamental/ requirement. The absence and the delay
>> reflects very badly on the C/C++ community.
>
> As I said, people managed fine without it.  Putting together a memory
> model that the C folks and C++ folks could agree on for all the
> platforms they support is not a trivial effort - and I am very glad they
> agreed here.  Of course I agree that it would have been nice to have had
> it earlier.  The thread support (as distinct from the atomic support,
> including memory models) is far too little, far too late and I doubt if
> it will have much use.

While there is no doubt people /thought/ they managed,
it is less clear cut that it was "fine".

I'm disappointed that thread support might not be as
useful as desired, but memory model and atomic is more
important.

Thread

Engineering degree for embedded systems "hogwarts" <122707@EmbeddedRelated> - 2017-07-27 07:35 -0500
  Re: Engineering degree for embedded systems Stef <stef33d@yahooI-N-V-A-L-I-D.com.invalid> - 2017-07-27 15:25 +0200
    Re: Engineering degree for embedded systems Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2017-07-30 12:05 -0400
      Re: Engineering degree for embedded systems Tom Gardner <spamjunk@blueyonder.co.uk> - 2017-07-30 19:05 +0100
        Re: Engineering degree for embedded systems Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2017-08-01 08:55 -0400
          Re: Engineering degree for embedded systems Tom Gardner <spamjunk@blueyonder.co.uk> - 2017-08-01 14:23 +0100
            Re: Engineering degree for embedded systems Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2017-08-03 11:03 -0400
              Re: Engineering degree for embedded systems Tom Gardner <spamjunk@blueyonder.co.uk> - 2017-08-06 10:35 +0100
                Re: Engineering degree for embedded systems John Devereux <john@devereux.me.uk> - 2017-08-06 14:40 +0100
                Re: Engineering degree for embedded systems rickman <gnuarm@gmail.com> - 2017-08-06 12:51 -0400
                Re: Engineering degree for embedded systems Tom Gardner <spamjunk@blueyonder.co.uk> - 2017-08-06 20:13 +0100
                Re: Engineering degree for embedded systems rickman <gnuarm@gmail.com> - 2017-08-06 19:21 -0400
                Re: Engineering degree for embedded systems Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2017-08-07 12:40 -0400
                Re: Engineering degree for embedded systems rickman <gnuarm@gmail.com> - 2017-08-07 15:18 -0400
                Re: Engineering degree for embedded systems Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2017-08-07 15:27 -0400
                Re: Engineering degree for embedded systems rickman <gnuarm@gmail.com> - 2017-08-07 16:47 -0400
                Re: Engineering degree for embedded systems Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2017-08-07 17:30 -0400
                Re: Engineering degree for embedded systems rickman <gnuarm@gmail.com> - 2017-08-07 18:35 -0400
                Re: Engineering degree for embedded systems Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2017-08-07 18:56 -0400
                Re: Engineering degree for embedded systems rickman <gnuarm@gmail.com> - 2017-08-07 19:02 -0400
                Re: Engineering degree for embedded systems Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2017-08-07 19:08 -0400
                Re: Engineering degree for embedded systems Hans-Bernhard Bröker <HBBroeker@t-online.de> - 2017-08-08 01:30 +0200
                Re: Engineering degree for embedded systems Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2017-08-07 19:32 -0400
                Re: Engineering degree for embedded systems rickman <gnuarm@gmail.com> - 2017-08-07 19:53 -0400
                Re: Engineering degree for embedded systems Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2017-08-07 20:02 -0400
                Re: Engineering degree for embedded systems stephen@mpeforth.com (Stephen Pelc) - 2017-08-07 23:49 +0000
                Re: Engineering degree for embedded systems Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2017-08-07 20:07 -0400
                Re: Engineering degree for embedded systems Tom Gardner <spamjunk@blueyonder.co.uk> - 2017-08-08 08:00 +0100
                Re: Engineering degree for embedded systems George Neuner <gneuner2@comcast.net> - 2017-08-07 01:21 -0400
                Re: Engineering degree for embedded systems upsidedown@downunder.com - 2017-08-06 17:15 +0300
                Re: Engineering degree for embedded systems Tom Gardner <spamjunk@blueyonder.co.uk> - 2017-08-06 20:21 +0100
                Re: Engineering degree for embedded systems upsidedown@downunder.com - 2017-08-07 10:35 +0300
                Re: Engineering degree for embedded systems David Brown <david.brown@hesbynett.no> - 2017-08-07 12:54 +0200
                Re: Engineering degree for embedded systems David Brown <david.brown@hesbynett.no> - 2017-08-07 12:34 +0200
                Re: Engineering degree for embedded systems Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2017-08-07 12:43 -0400
                Re: Engineering degree for embedded systems rickman <gnuarm@gmail.com> - 2017-08-06 12:50 -0400
                Re: Engineering degree for embedded systems Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2017-08-07 12:36 -0400
                Re: Engineering degree for embedded systems Tom Gardner <spamjunk@blueyonder.co.uk> - 2017-08-07 18:40 +0100
                Re: Engineering degree for embedded systems David Brown <david.brown@hesbynett.no> - 2017-08-08 10:23 +0200
                Re: Engineering degree for embedded systems Tom Gardner <spamjunk@blueyonder.co.uk> - 2017-08-08 09:46 +0100
                Re: Engineering degree for embedded systems David Brown <david.brown@hesbynett.no> - 2017-08-08 11:26 +0200
                Re: Engineering degree for embedded systems Tom Gardner <spamjunk@blueyonder.co.uk> - 2017-08-08 11:09 +0100
                Re: Engineering degree for embedded systems David Brown <david.brown@hesbynett.no> - 2017-08-08 12:56 +0200
                Re: Engineering degree for embedded systems Tom Gardner <spamjunk@blueyonder.co.uk> - 2017-08-08 15:56 +0100
                Re: Engineering degree for embedded systems David Brown <david.brown@hesbynett.no> - 2017-08-08 17:11 +0200
                Re: Engineering degree for embedded systems Tom Gardner <spamjunk@blueyonder.co.uk> - 2017-08-08 16:33 +0100
                Re: Engineering degree for embedded systems upsidedown@downunder.com - 2017-08-08 21:07 +0300
                Re: Engineering degree for embedded systems David Brown <david.brown@hesbynett.no> - 2017-08-09 10:03 +0200
                Re: Engineering degree for embedded systems upsidedown@downunder.com - 2017-08-10 14:30 +0300
                Re: Engineering degree for embedded systems David Brown <david.brown@hesbynett.no> - 2017-08-10 15:11 +0200
                Re: Engineering degree for embedded systems Walter Banks <walter@bytecraft.com> - 2017-08-16 18:39 -0400
                Re: Engineering degree for embedded systems David Brown <david.brown@hesbynett.no> - 2017-08-17 09:37 +0200
                Re: Engineering degree for embedded systems Walter Banks <walter@bytecraft.com> - 2017-08-17 08:24 -0400
                Re: Engineering degree for embedded systems David Brown <david.brown@hesbynett.no> - 2017-08-17 16:06 +0200
                Re: Engineering degree for embedded systems Walter Banks <walter@bytecraft.com> - 2017-08-17 12:15 -0400
                Re: Engineering degree for embedded systems David Brown <david.brown@hesbynett.no> - 2017-08-18 14:45 +0200
                Re: Engineering degree for embedded systems Walter Banks <walter@bytecraft.com> - 2017-08-25 09:51 -0400
          Re: Engineering degree for embedded systems Les Cargill <lcargill99@comcast.com> - 2017-08-01 20:46 -0500
            Re: Engineering degree for embedded systems David Brown <david.brown@hesbynett.no> - 2017-08-02 09:30 +0200
              Re: Engineering degree for embedded systems Les Cargill <lcargill99@comcast.com> - 2017-08-05 15:11 -0500
              Re: Engineering degree for embedded systems Paul Rubin <no.email@nospam.invalid> - 2017-08-08 00:22 -0700
                Re: Engineering degree for embedded systems Tom Gardner <spamjunk@blueyonder.co.uk> - 2017-08-08 08:36 +0100
                Re: Engineering degree for embedded systems David Brown <david.brown@hesbynett.no> - 2017-08-08 12:37 +0200
  Re: Engineering degree for embedded systems "tim..." <tims_new_home@yahoo.com> - 2017-07-27 17:46 +0100
    Re: Engineering degree for embedded systems Grant Edwards <invalid@invalid.invalid> - 2017-07-27 16:54 +0000
      Re: Engineering degree for embedded systems "tim..." <tims_new_home@yahoo.com> - 2017-07-27 19:57 +0100
  Re: Engineering degree for embedded systems Frank Miles <fpm@u.washington.edu> - 2017-07-27 16:58 +0000
    Re: Engineering degree for embedded systems Theo Markettos <theom+news@chiark.greenend.org.uk> - 2017-07-28 00:43 +0100
    Re: Engineering degree for embedded systems jim.brakefield@ieee.org - 2017-07-30 15:26 -0700
  Re: Engineering degree for embedded systems Chris <xxx.syseng.yyy@gfsys.co.uk> - 2017-07-27 23:45 +0000
  Re: Engineering degree for embedded systems Hans-Bernhard Bröker <HBBroeker@t-online.de> - 2017-08-03 19:50 +0200
    Re: Engineering degree for embedded systems Les Cargill <lcargill99@comcast.com> - 2017-08-05 15:20 -0500
      Re: Engineering degree for embedded systems upsidedown@downunder.com - 2017-08-06 09:17 +0300
        Re: Engineering degree for embedded systems "tim..." <tims_new_home@yahoo.com> - 2017-08-06 10:12 +0100
          Re: Engineering degree for embedded systems upsidedown@downunder.com - 2017-08-06 13:19 +0300
          Re: Engineering degree for embedded systems Les Cargill <lcargill99@comcast.com> - 2017-08-06 09:59 -0500
            Re: Engineering degree for embedded systems "tim..." <tims_new_home@yahoo.com> - 2017-08-06 18:06 +0100
              Re: Engineering degree for embedded systems rickman <gnuarm@gmail.com> - 2017-08-06 21:31 -0400
                Re: Engineering degree for embedded systems "tim..." <tims_new_home@yahoo.com> - 2017-08-07 09:32 +0100
        Re: Engineering degree for embedded systems Les Cargill <lcargill99@comcast.com> - 2017-08-06 09:53 -0500
          Re: Engineering degree for embedded systems upsidedown@downunder.com - 2017-08-07 10:59 +0300
            Re: Engineering degree for embedded systems Les Cargill <lcargill99@comcast.com> - 2017-08-07 20:09 -0500
              Re: Engineering degree for embedded systems upsidedown@downunder.com - 2017-08-08 21:31 +0300
        Re: Engineering degree for embedded systems Stef <stef33d@yahooI-N-V-A-L-I-D.com.invalid> - 2017-08-21 11:28 +0200

csiph-web