Any reason why they stopped at 2 threads per core? Why not 4

Diminishing returns

Look up IBM SMT4 and SMT8 on Power8 and Power9.

Simultaneous multithreading is only really useful if your CPU has the resources to actually deal with that many concurrent threads, which means lots of FPUs, large caches, etc.

>>56272572
>Any reason why they stopped at 2 threads per core?
where the fuck are you pulling that shit from ? they didn't stop at 2 threads per core

>>56272572
Threads share the hardware on a core. Its hard enough to make use of 2 threads properly per core. Ie so each thread doesn't use the same resource. Apart from some very specific tasks, it probably wasn't worth doing more than 2.

>>56272595
In reference to Intel / new AMD cpus I think OP means.

>>56272595
Stay in /v/
>>56272609
He posted a pic very clearly referencing intel's Hyperthreading

>>56272572
SMT exists to under-utilized pipelines in a processor. If you run a single thread you get some pipeline stalls when it waits for memory, can't reorder chains of data-depedencies, waits for high-latency instructions etc.

Running two threads can fill those gaps with the stuff another thread does at a moderate cost of resource increase. You "only" have to duplicate some things like the register sets and not the whole pipeline.

Adding even more threads would turn the non-redundant resources into the bottleneck.

>>56272609
xeon phi have 4 threads per core

>>56272621
xeon phis use hyperthreading too, dipshit

File: 1443406711169.png (973KB, 801x1500px) Image search: [Google]

973KB, 801x1500px

>>56272572
Oh i dunno...

>>56272572

More importantly; why is Intel cheating the OS to think there are double the cores available? HyperThreading should be available as x86-64 instructions for high performance software and games, and not something the OS should control or use.

>>56273145
are you legitimately retarded or just pretending in order to troll?

>>56273169

It's a legit question.

>>56273178
How is it a legit question? In an i7-6700k there are 4 physical cores each with 2 logical cores and resources to share between the two. The OS isn't being tricked or cheated, as far as it's concerned it has 8 threads it can take advantage of.

>>56273145

it's not cheating the OS. you need your cpu scheduler to actually be optimzied for SMT to get gains from it.

>>56273230
OS needs to be enabled of HT support. No HT for any application if OS doesn't support it.

>>56274815
Okay? Your point is what?

There is no lying or cheating going on, if you dont understand what's being discussed just leave.

>>56272572
Because HT is a meme technology which barely gives you gains with 2 threads per core. Adding 4 threads per core would just complicate the design while giving even less gain per thread than the current HT.

>>56274987
>Because HT is a meme technology which barely gives you gains with 2 threads per core.

This is simply not true. For applications optimized for multi-threading speedup can be close to 2 times.

>>56272572
It's not particularly useful on general workloads, the gain from it diminishes with more threads. IBM Power processors use more threads per core but they're purpose-built.