Path: ...!weretis.net!feeder9.news.weretis.net!i2pn.org!i2pn2.org!.POSTED!not-for-mail
From: mhx@iae.nl (mhx)
Newsgroups: comp.lang.forth
Subject: Re: Parallel Forth on a 44 core machine
Date: Sun, 18 Aug 2024 13:33:27 +0000
Organization: novaBBS
Message-ID: <932f13f537e8c918ecd2089466e4c405@www.novabbs.com>
References: <a46cb8e455c12e2c81cd2ff60c095528@www.novabbs.com> <112ba13cc3d99496d5825773b3f0642e@www.novabbs.com> <2df471d1ec39c22949169f8a612b780d@www.novabbs.com> <nnd$0f8813aa$41d0ee61@18dd570284c2b77b>
MIME-Version: 1.0
Content-Type: text/plain; charset=utf-8; format=flowed
Content-Transfer-Encoding: 8bit
Injection-Info: i2pn2.org;
	logging-data="3008298"; mail-complaints-to="usenet@i2pn2.org";
	posting-account="t0bSWFIQDvYvkkhDiPIIv6byulC6WbSEwXWMJpxc4k0";
User-Agent: Rocksolid Light
X-Rslight-Site: $2y$10$HRfK0/bMTwbf9kyBcYFZGu0pDZIp70jnPJo5qXVzLyV7YPf84ye.m
X-Rslight-Posting-User: 59549e76d0c3560fb37b97f0b9407a8c14054f24
X-Spam-Checker-Version: SpamAssassin 4.0.0
Bytes: 2543
Lines: 33

On Sun, 18 Aug 2024 12:47:39 +0000, albert@spenarnc.xs4all.nl wrote:

> In article <2df471d1ec39c22949169f8a612b780d@www.novabbs.com>,
> mhx <mhx@iae.nl> wrote:
[..]
>>A new (to me) thing was that processes slow down enormously from
>>accessing shared global variables (depending on their physical
>>location), even when no locks are needed/used. For iSPICE such
>>variables are in OS managed shared memory (aka the swap file)
>>and are used very infrequently.
>
> That agrees with my experience. Parallel processes work with the
> same image. The protocol is that one process write to a shared variable,
> the other reads. The last process signals the chain that it is
> ready. All processes are busy waiting on the signal to stop and to
> pass it down the chain.
>
> That was on linux with AMD.
> Was your experience MS with Intel?

What you seem to describe is that processes interfere when wanting
access to the same (multi-byte) variable. It is obviously tricky to
read a value byte-by-byte when somebody else is updating it
byte-by-byte.
What I meant is severe slowdown when reading variables that are
physically *close* to variables that belong to another process.
It happens for both AMD and Intel on both Windows and Linux.
Spacing such variables farther apart has dramatic impact but
is quite inconvenient in most cases.

I don't recall that transputers had these problems. It may have
to do with the physical memory read/write hardware.

-marcel