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From: mhx@iae.nl (mhx)
Newsgroups: comp.lang.forth
Subject: Re: Parallel Forth on a 44 core machine
Date: Sun, 18 Aug 2024 11:31:37 +0000
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On Sun, 18 Aug 2024 9:28:09 +0000, minforth wrote:

> Impressive! A PCIe NVMe drive will be a boost, but don't expect
> too much, when you already have so much RAM. And electric power. ;-)

I tried a RAM drive (from AMD), but it has a throughput of only 50MB/s,
10x slower than the SATA 6GBs connected Samsung SSD (500MB/s). I am a
bit puzzled why that is so devastatingly slow.

> My experiments with parallel threads were a bit sobering. You
> really need rather isolated subprocesses that require little
> synchronisation.

Yes, that is Amdahl's law. We constantly struggled with that
for tForth. Fine-grained parallelism never gave us good results.

> Otherwise the slowest process plus additional
> syncing costs can eat up all the expected benefits. Nothing new.

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.

-marcel