2 Oct
2019
2 Oct
'19
6:59 p.m.
On Tue, 17 Sep 2019, Jon Elson via cctalk wrote:
The NVAX and NVAX+ implementations include a branch predictor in their
microarchitecture[1], so obviously they do execute speculatively.
"Spectre" is one of two notorious bugs of modern CPUs involving speculative
execution. I rather doubt that VAX is affected by this but I suspect others
here have a lot more knowledge.
You need an extremely high resolution timer to detect slight differences in
execution time of speculatively-executed threads. The VAX 11/780 certainly did
not do speculative execution, and my guess is that all VAXen did not, either. Also, I don't think the timer was high enough
resolution to detect such a
difference.
I can't speak of timer availability offhand though.
References:
[1] G. Michael Uhler et al, "The NVAX and NVAX+ High-performance VAX
Microprocessors", Digital Technical Journal Vol. 4 No. 3 Summer 1992
<ftp://ftp.linux-mips.org/pub/linux/mips/people/macro/DEC/DTJ/DTJ701/DTJ701PF.PDF>
Maciej