Processors

[Arzel]

What is a hyperthreaded processor how is it different from a normal i5,i7 etc? How many cores and thread count do general processor have and if given the no of cores how would you find the no of threads in each core in a normal processor? Thank you.

[Electronics Wizardy]

Hyperthreading/SMT allows 2 threads to run on one core at one, better filling the processor pipeline. Normally you get upto 30% more performance in heavly multithreaded apps on x86 chips. 

[emosun]

and to see how many cores a cpu has and what cores have hyperthreading....which is all of them , you can very easily google a spec sheet for the cpu that lists the information on it.

[MVPernula]

Hi there!

 

Hyperthreading basically means your CPU has 'logical cores'.

Say that "weaker/cheaper" CPU's only have 2 *physical* cores, but 4 logical ones. It boosts performance but it cheaper than having 4 logical cores.

 

I5's and i7's also have hyperthreading (sometimes, not all cases), to boost their general performance.

I will refer cores as 'c' and threads (which is hyperthreading), as 't'.

So a 4 core, 8 threaded CPU would be 4c/8t.

 

THere isn't a standard to how many cores and threads a specific CPU has, it depends on pricarange and purpose. We have budget 2c/2t CPU's and 26c/52t CPu's. And more cores =/= better gaming performance.

In some cases the 2/2 would win pover the 26/52 in gaming due to speeds and such.

 

Linus has made good videos about the differences on intels side of things. (i3-i7)

check it out!

[3 Lions]

Watch this...

 

[Mira Yurizaki]

33 minutes ago, Arzel said:

What is a hyperthreaded processor how is it different from a normal i5,i7 etc?

This is going to be a long read, so brew some coffee, get comfy, and relax.

 

The first thing you need to know about this is what a thread is. A thread is basically a task that an application wants to do independently of other tasks. For example in your web browser, there are a few threads it will create to handle:

• The user interface
• Networking (like sending or receiving things)
• HTML rendering
• JavaScript execution

The reason why applications create threads is if the web browser ran on a single thread and it needs to get something from a web server, the application cannot do anything else until a response from the server comes back. This makes the browser unresponsive. By creating a separate thread to handle that, you can put the thread to sleep until a response comes back from the server, allowing other threads to be worked on. When it comes to executing these threads on the CPU, it's the OS's job to schedule that. So for most modern OSes, the OS doesn't schedule the actual application to run, it only schedules its threads.

 

Now on the processor itself, in order to execute more and more instructions, engineers put in more execution units. These execution units can perform a specific task like doing basic integer arithmetic, calculating a memory address, or do some floating point math (integer and floating point math are separated for performance reasons). But sometimes a thread can't use all of these execution resources. Like one thread only wants to add some integer numbers while another only wants to do floating point math.

 

This is where Hyperthreading comes in. In order to utilize these execution resources as much as possible, Hyperthreaded processors can run two or more threads at once depending on what execution resources are available. In the previous paragraph, a Hyperthreaded processor can do both of those threads, because they don't use the same execution resource and can run in parallel. To the OS, a Hyperthreaded processor looks like every CPU core has two or more cores in it. Though some things of note here, Hyperthreading is a trade name by Intel. The generic name for this is called Simultaneous Multithreading or SMT. And while Hyperthreading is often implemented by allowing up to two threads per core, some implementations allow for more. The Xeon Phi has 4-thread Hyperthreading for instance.

 

While it sounds good on paper, in practice, the performance boost Hyperthreading and SMT in general provides is a mixed bag. Remember, those threads have to share the same pool of execution resources, and threads can still use multiple resources at once if it can. If it helps, it's better to think of this like a factory. One job may require 4 out of the 7 workers you have, leaving 3 to do other things. But another job may require all 7.

 

But to answer "how is it different from a normal i5, i7, etc.?", i5 processors are usually i7 processors without Hyperthreading. But otherwise, it either has Hyperthreading or it doesn't.

 

33 minutes ago, Arzel said:

How many cores and thread count do general processor have and if given the no of cores how would you find the no of threads in each core in a normal processor? Thank you.

Unless the processor implements some form of SMT, it can only do one thread per core. As far as the core count goes, it depends on what model of processor you're looking at.

[geo3]

Hyper-threading is Intel's market name for it's implementation of SMT.

 

SMT allows each physical core on a CPU to run 2 tasks(threads) at the same time. So a SMT enabled chip will be able to run a number of tasks that's 2x the number of cores it has.

 

For desktop class processors i3 and i5 don't have SMT, i7 does. But that's little different on mobile processors where i3 can sometimes have SMT.

[pas008]

typically its 2 threads per core for ht/smt

 

but xeon phi series have 4 thread per core

which we may see in the future

 

 

[Mira Yurizaki]

7 minutes ago, pas008 said:

but xeon phi series have 4 thread per core

which we may see in the future

That may not really happen. Adding SMT is only useful for highly parallelized operations. I also could've sworn I read that the only reason why Xeon Phi has 4-thread SMT is it's cheaper to maintain more thread states than it is to context switch due to the ring-bus design.

[pas008]

6 minutes ago, M.Yurizaki said:

That may not really happen. Adding SMT is only useful for highly parallelized operations. I also could've sworn I read that the only reason why Xeon Phi has 4-thread SMT is it's cheaper to maintain more thread states than it is to context switch due to the ring-bus design.

true I wont rule it out just yet considering we may be having a core/thread war starting up

wouldnt be hard for either company to implement

[Mira Yurizaki]

2 minutes ago, pas008 said:

true I wont rule it out just yet considering we may be having a core/thread war starting up

wouldnt be hard for either company to implement

I'm also debating if that's going to be a thing. Applications most people use on a day-to-day basis are I/O bound and adding more cores won't help.

 

Though may be it will with the dozens of things people seem to find a need to run at once.