4 ms·

I don't think weak memory models are inherently bad. It's a trade-off. Keep in mind it was conceived during the early days of SMP - there wasn't the industry pr

I don't think weak memory models are inherently bad. It's a trade-off. Keep in mind it was conceived during the early days of SMP - there wasn't the industry preference for stronger models, which was largely a side-effect of x86 chips choosing that approach with SMP years later.

hinkley 3y ago
And everyone wanting to be able to claim top shelf Java support. Say what you will about Java, but a lot of OSes and hardware had to get a lot better at multithreading pretty quickly or be relegated. Even Solaris struggled for a time.
chasil 3y ago
> "early days of SMP" This is vastly incorrect. UNIX was ported to the Univac architecture in the late '70s. It ran as a client on EXEC 8, and was the first SMP implementation. "The UNIVAC 1108 computer was announced in 1964 and delivered in late 1965. The first 1108 computers used Exec I and Exec II, which had been developed for the UNIVAC 1107. However, UNIVAC planned to offer symmetric multiprocessor versions of the 1108 with up to 4 processors and the earlier operating systems (really basic monitor programs) weren't designed for that, even though they supported limited multiprogramming." https://en.wikipedia.org/wiki/OS_2200 https://en.wikipedia.org/wiki/OS_2200
- spamizbad 3y ago
  The 1108 had simplistic memory protection and didn't have cache so there was no concerns around cache coherency. The 1100/80 which came 15 years later finally introduced a cache that was really just a buffer and, to my knowledge, had no coherency scheme largely because of the way the architecture of those systems worked. The Alpha team was working on a much more sophisticated system and had to solve a much coherency problem. Weaker models allow greater throughput and save transistors (and reduce power/heat) at the expense of more carefully written software and operating systems.

hinkley 3y ago

And everyone wanting to be able to claim top shelf Java support. Say what you will about Java, but a lot of OSes and hardware had to get a lot better at multithreading pretty quickly or be relegated. Even Solaris struggled for a time.

chasil 3y ago

> "early days of SMP" This is vastly incorrect. UNIX was ported to the Univac architecture in the late '70s. It ran as a client on EXEC 8, and was the first SMP implementation. "The UNIVAC 1108 computer was announced in 1964 and delivered in late 1965. The first 1108 computers used Exec I and Exec II, which had been developed for the UNIVAC 1107. However, UNIVAC planned to offer symmetric multiprocessor versions of the 1108 with up to 4 processors and the earlier operating systems (really basic monitor programs) weren't designed for that, even though they supported limited multiprogramming." https://en.wikipedia.org/wiki/OS_2200 https://en.wikipedia.org/wiki/OS_2200

spamizbad 3y ago
The 1108 had simplistic memory protection and didn't have cache so there was no concerns around cache coherency. The 1100/80 which came 15 years later finally introduced a cache that was really just a buffer and, to my knowledge, had no coherency scheme largely because of the way the architecture of those systems worked. The Alpha team was working on a much more sophisticated system and had to solve a much coherency problem. Weaker models allow greater throughput and save transistors (and reduce power/heat) at the expense of more carefully written software and operating systems.