From: downing.nick@gmail.com (Nick Downing)
Subject: [TUHS] Another odd comment in V6
Date: Wed, 15 Feb 2017 01:18:29 +1100 [thread overview]
Message-ID: <CAH1jEzYCWh7ZGMfhFKeObdkSJN09AO9PUq6S-3Npv_Jdvndvsg@mail.gmail.com> (raw)
In-Reply-To: <868tp8kgxo.fsf@molnjunk.nocrew.org>
Excellent paper, well that makes it completely clear what the MIT guy
means by restarting a system call. It is interesting that in their
approach they restart a read() or write() call or whatever they call
it in their system, with the buffer advanced and the count reduced.
This is a bit like what would happen in x86 if it gets interrupted in
a REP MOVSB instruction, it returns into REP MOVSB with SI/DI advanced
and CX reduced. However it would not work exactly right in unix due to
the return value from read()/write() being wrong. Anyway, I like the
unix way, it is nice and simple. I have never found it to be a problem
when devices return a "short read" or "short write", although it is an
interesting semantic that if you opened the file yourself and you're
doing lseek on it, it cannot be a TTY, and short reads/writes do not
occur. Having a hypothetical system with a very slow disk (or fast
CPU) in which disk accesses are blocking, would break many programs.
cheers, Nick
On Wed, Feb 15, 2017 at 1:03 AM, Lars Brinkhoff <lars at nocrew.org> wrote:
> Nick Downing <downing.nick at gmail.com> writes:
>> By contrast the MIT guy probably was working with a much smaller/more
>> economical system that didn't maintain a kernel stack per process.
>
> No. PCLSRing is a feature of MIT' ITS operating system, and it does
> have a separate stack for the kernel.
>
> Here is a copy of Alan Bawdens paper about PCLSRing:
> http://fare.tunes.org/tmp/emergent/pclsr.htm
next prev parent reply other threads:[~2017-02-14 14:18 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-02-14 8:46 Paul Ruizendaal
2017-02-14 11:27 ` Nick Downing
2017-02-14 12:27 ` Paul Ruizendaal
2017-02-14 12:46 ` Nick Downing
2017-02-14 14:03 ` Lars Brinkhoff
2017-02-14 14:18 ` Nick Downing [this message]
2017-02-14 15:50 ` Random832
2017-02-14 14:14 Noel Chiappa
2017-02-14 14:35 ` Paul Ruizendaal
2017-02-14 15:48 ` Random832
2017-02-14 16:06 ` Dan Cross
2017-02-14 15:40 Noel Chiappa
2017-02-14 16:17 Noel Chiappa
2017-02-21 19:23 Norman Wilson
2017-02-22 9:59 ` Tony Finch
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