Hyperthreading intel processors and C

Question

If I don't utilize multithreaded paradigms when designing my code, will hyperthreading split the load automagically over the logical cores, or would my have to be specicially written to take advantage of the other cores like it would have to be for physical cores?

Answer 1

On suggestion of @us2012 I post this here from my comment...

There is no such magic. Superscalar CPUs, especially OOO (Out Of Order execution) processors do magic - but that is inside one core.

On the contrary, Hyperthreading can be thought of as (very simplified) two pipelines in front of one complete core.

AMD Bulldozer CPUs have a similar bit, but they went a step further: the integer core is split into two too, but the two pipelines + integer cores share one floating point unit. This whole is called a "module", having two threads.

TL;DR

Superscalar (from the Wiki)

A superscalar CPU architecture implements a form of parallelism called instruction level parallelism within a single processor. It therefore allows faster CPU throughput than would otherwise be possible at a given clock rate. A superscalar processor executes more than one instruction during a clock cycle by simultaneously dispatching multiple instructions to redundant functional units on the processor. Each functional unit is not a separate CPU core but an execution resource within a single CPU such as an arithmetic logic unit, a bit shifter, or a multiplier.

Out of order execution (from the Wiki)

In computer engineering, out-of-order execution (OoOE or OOE) is a paradigm used in most high-performance microprocessors to make use of instruction cycles that would otherwise be wasted by a certain type of costly delay. In this paradigm, a processor executes instructions in an order governed by the availability of input data, rather than by their original order in a program. In doing so, the processor can avoid being idle while data is retrieved for the next instruction in a program, processing instead the next instructions which are able to run immediately.

Hyperthreading (from... you know where...)

Hyper-threading (officially Hyper-Threading Technology or HT Technology, abbreviated HTT or HT) is Intel's proprietary simultaneous multithreading (SMT) implementation used to improve parallelization of computations (doing multiple tasks at once) performed on PC microprocessors. It first appeared in February 2002 on Xeon server processors and in November 2002 on Pentium 4 desktop CPUs.1 Later, Intel included this technology in Itanium, Atom, and Core 'i' Series CPUs, among others.

Bulldozer (not from not the wiki)

Bulldozer is the first major redesign of AMD’s processor architecture since 2003, when the firm launched its K8 processors, and also features two 128-bit FMA-capable FPUs which can be combined into one 256-bit FPU. This design is accompanied by two integer clusters, each with 4 pipelines (the fetch/decode stage is shared). Bulldozer will also introduce shared L2 cache in the new architecture. AMD's marketing service calls this design a "Module". A 16-threads processor design would feature eight of these "modules",[7] but the operating system will recognize each "module" as two logical cores.