Bill wrote:
Paul wrote:
THe (T) part measures Hyperthreading,
which helps 7ZIP a bit. But it's the C number that bears most
of the weight when doing 7ZIP (or RAR) compression.
Do all of the newer CPUs offer Hyperthreading (or something equivalent)?
I'm not exactly sure what it is, but I presume it enables multiple
threads to run faster on a single core. For example, do the new AMD
CPUs have hyperthreading (or something equivalent)?

Cheers,
Bill

Register Bank Register Bank
| |
select between them
|
out of order
execution engine

What HyperThreading does, is if the CPU core is
"stalled" on a memory access (a wait of 100 cycles
say), the core can switch to the other bank, where
the other bank is not stalled, and execution of
a thread there can take place. Now, if that
register bank happens to need a memory access, it
stalls, and the engine flips back to the other
side (where the required memory access if finished).

For the price of a suitably large register bank,
you can extract anywhere from -5% to +30% more
performance. On a multi-threaded application.

AMD calls this SMT. You'd have to look somewhere,
to see whether this is exactly the same mechanism
as Intel uses.

A Russian site added some color on the topic. They
found that the Pentium with this feature, had a
"recirculator loop", and some information sits in
a queue while this sort of switching is going on.
And apparently the first HT had a bug, where the
recirculator could sorta hang for a millisecond.
And nobody noticed. Later HT implementations
were better than the first one. But then the later
ones never got any color commentary like that.

*******

There are certain usage patterns, that cause thrashing
or competition between the two sides and rob the CPU
of performance (-5%). In some cases, users elect on their
16C 32T processor, to turn off the 32T and just run
with the 16C. If you have a 64C 128T processor (they exist),
if you switch on the 128T, Windows treats this as
"two processor groups" and weird stuff happens. Again,
the better part of valor might be to turn off the
128T portion so the scheduler in Windows behaves itself.
Windows 10 Workstation does better scheduling than
Windows 10 Pro (you might find that mentioned on
the enthusiast sites I saw that in). So not all the
Windows SKUs are equal.

Paul