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| From | anton@mips.complang.tuwien.ac.at (Anton Ertl) |
|---|---|
| Newsgroups | comp.lang.forth |
| Subject | Re: Parallel Forth on a 44 core machine |
| Date | 2024-08-18 13:42 +0000 |
| Organization | Institut fuer Computersprachen, Technische Universitaet Wien |
| Message-ID | <2024Aug18.154233@mips.complang.tuwien.ac.at> (permalink) |
| References | <a46cb8e455c12e2c81cd2ff60c095528@www.novabbs.com> <112ba13cc3d99496d5825773b3f0642e@www.novabbs.com> <2df471d1ec39c22949169f8a612b780d@www.novabbs.com> <nnd$0f8813aa$41d0ee61@18dd570284c2b77b> <932f13f537e8c918ecd2089466e4c405@www.novabbs.com> |
mhx@iae.nl (mhx) writes:
>What I meant is severe slowdown when reading variables that are
>physically *close* to variables that belong to another process.
That is known as false sharing. The cache coherence protocols work at
the granularity of a a cache line (usually 64 bytes). If core A
writes to a variable, and core B, say, reads one in the same cache
line, the cache coherence protocol first makes that cache line
modified by core A (and every other core has to invalidate that cache
line), and then core B has to wait until core A sends out the data to
the other cores.
>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.
Yes, but if you want performance, you have to rearrange your data to
avoid false sharing.
>I don't recall that transputers had these problems.
Transputers have no shared memory and therefore no cache coherence
protocols.
- anton
--
M. Anton Ertl http://www.complang.tuwien.ac.at/anton/home.html
comp.lang.forth FAQs: http://www.complang.tuwien.ac.at/forth/faq/toc.html
New standard: https://forth-standard.org/
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Parallel Forth on a 44 core machine mhx@iae.nl (mhx) - 2024-08-17 15:34 +0000
Re: Parallel Forth on a 44 core machine minforth@gmx.net (minforth) - 2024-08-18 09:28 +0000
Re: Parallel Forth on a 44 core machine mhx@iae.nl (mhx) - 2024-08-18 11:31 +0000
Re: Parallel Forth on a 44 core machine albert@spenarnc.xs4all.nl - 2024-08-18 14:47 +0200
Re: Parallel Forth on a 44 core machine mhx@iae.nl (mhx) - 2024-08-18 13:33 +0000
Re: Parallel Forth on a 44 core machine anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2024-08-18 13:42 +0000
Re: Parallel Forth on a 44 core machine mhx@iae.nl (mhx) - 2024-08-18 14:32 +0000
Re: Parallel Forth on a 44 core machine anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2024-08-18 15:14 +0000
Re: Parallel Forth on a 44 core machine minforth@gmx.net (minforth) - 2024-08-18 14:01 +0000
Re: Parallel Forth on a 44 core machine mhx@iae.nl (mhx) - 2024-08-28 09:29 +0000
Re: Parallel Forth on a 44 core machine Paul Rubin <no.email@nospam.invalid> - 2024-08-28 09:35 -0700
Re: Parallel Forth on a 44 core machine mhx@iae.nl (mhx) - 2024-08-18 18:37 +0000
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