Once upon a time, to write x86 assembler, for example, you would have instructions stating &quot;load the EDX register with the value 5&quot;, &quot;increment the EDX&quot; register, etc.

With modern CPUs that have 4 cores (or even more), at the machine code level does it just look like there are 4 separate CPUs (i.e. are there just 4 distinct &quot;EDX&quot; registers) ?  If so, when you say &quot;increment the EDX register&quot;, what determines which CPU&#39;s EDX register is incremented? Is there a &quot;CPU context&quot; or &quot;thread&quot; concept in x86 assembler now?

How does communication/synchronization between the cores work?

If you were writing an operating system, what mechanism is exposed via hardware to allow you to schedule execution on different cores? Is it some special priviledged instruction(s)?

If you were writing an optimizing compiler/bytecode VM for a multicore CPU, what would you need to know specifically about, say, x86 to make it generate code that runs efficiently across all the cores?

What changes have been made to x86 machine code to support multi-core functionality?

What does multicore assembly language look like?

Quick question: what is the compiler flag to allow g++ to spawn multiple instances of itself in order to compile large projects quicker (for example 4 source files at a time for a multi-core CPU)?


Compiling with g++ using multiple cores

What&#39;s the status of multicore programming in Haskell? What projects, tools, and libraries are available now? What experience reports have there been?

What&#39;s the status of multicore programming in Haskell?

Is there any way to measure a specific process CPU usage by cores?

I know [top][1] is good for measuring the whole system&#39;s CPU usage by cores and [taskset][2] can provide information about which CPU core is allowed for the process to run on.

But how do I measure a specific process&#39; CPU usage by CPU cores?

  [1]: http://en.wikipedia.org/wiki/Top_%28software%29
  [2]: http://linux.die.net/man/1/taskset



How do I measure separate CPU core usage for a process?

I&#39;m working on a multithreaded application, and I want to debug it using GDB.

Problem is, one of my threads keeps dying with the message:

    pure virtual method called
    terminate called without an active exception
    Abort

I know the cause of that message, but I have no idea where in my thread it occurs. A backtrace would really be helpful.

When I run my app in GDB, it pauses every time a thread is suspended or resumed. I want my app to continue running normally until one of the threads dies with that exception, at which point everything should halt so that I can get a backtrace.

Run an Application in GDB Until an Exception Occurs

Could anyone explain to me the differences between multi-CPU, multi-core, and hyper-thread? I am always confused about these differences, and about the pros/cons of each architecture in different scenarios.

Here is my current understanding after learning online and learning from others&#39; comments.

1. I think hyper-thread is the most inferior technology among them, but cheap. Its main idea is duplicate registers to save context switch time;
2. Multi processor is better than hyper-thread, but since different CPUs are on different chips, the communication between different CPUs is of longer latency than multi-core, and using multiple chips, there is more expense and more power consumption than with multi-core;
3. multi-core integrates all the CPUs on a single chip, so the latency of communication between different CPUs are greatly reduced compared with multi-processor. Since it uses one single chip to contain all CPUs, it consumer less power and is less expensive than a multi processor system.

Is this correct?

What are the differences between multi-CPU, multi-core and hyper-thread?

I really like these tools when it comes to the concurrency level it can handle.

Erlang/OTP looks like much more stable solution but requires much more learning and a lot of diving into functional language paradigm. And it looks like Erlang/OTP makes it much better when it comes to multi-core CPUs (correct me  if I am wrong).

But which should I choose? Which one is better in the short and long term perspective?

My goal is to learn a tool which makes scaling my Web projects under high load easier than traditional languages.

Node.js or Erlang

What is the difference between multiprocessor programming and multicore programming?
preferably show examples in python how to write a small program for multiprogramming &amp; multicore programming

Does python support multiprocessor/multicore programming?

I&#39;m writing a Java program which uses a lot of CPU because of the nature of what it does.  However, lots of it can run in parallel, and I have made my program multi-threaded. When I run it, it only seems to use one CPU until it needs more then it uses another CPU - is there anything I can do in Java to force different threads to run on different cores/CPUs?

Forcing multiple threads to use multiple CPUs when they are available

I have heard that in Haskell, creating a multi-threaded application is as easy as taking a standard Haskell application and compiling it with the `-threaded` flag. Other cases, however, have described the use of a `par` command within the actual source code.

What is the state of Haskell multi-threading? How easy is it to introduce into programs? Is there a good multi-threading tutorial that goes over these different commands and their uses?

How difficult is Haskell multi-threading?

I have noticed that R only uses one core while executing one of my programs which requires lots of calculations. I would like to take advantage of my multi-core processor to make my program run faster.
I have not yet investigated the question in depth but I would appreciate to benefit from your comments because I do not have good knowledge in computer science and it is difficult for me to get easily understandable information on that subject.

Is there a package that allows R to automatically use several cores when needed?

I guess it is not that simple.

R package that automatically uses several cores?

Two new keywords added to the C# 5.0 language are [async](http://msdn.microsoft.com/en-us/library/hh156513(v=vs.110).aspx) and [await](http://msdn.microsoft.com/en-us/library/hh156528(v=vs.110).aspx), both of which work hand in hand to run a C# method asynchronously without blocking the calling thread.

My question is, do these methods actually take advantage of multiple cores and run in parallel or does the async method run in the same thread core as the caller? 

Do the new C# 5.0 &#39;async&#39; and &#39;await&#39; keywords use multiple cores?

As someone in the world of [HPC][1] who came from the world of enterprise web development, I&#39;m always curious to see how developers back in the &quot;real world&quot; are taking advantage of parallel computing.  This is much more relevant now that [all chips are going multicore][2], and it&#39;ll be even more relevant when there are thousands of cores on a chip instead of just a few.

My questions are: 

  1. How does this affect your software roadmap?
  1. I&#39;m particularly interested in real stories about how multicore is affecting different software domains, so specify what kind of development you do in your answer (*e.g.* server side, client-side apps, scientific computing, etc).
  1. What are you doing with your existing code to take advantage of multicore machines, and what challenges have you faced?  Are you using [OpenMP][3], [Erlang][4], [Haskell][5], [CUDA][6], [TBB][7], [UPC][8] or something else?
  1. What do you plan to do as concurrency levels continue to increase, and how will you deal with hundreds or thousands of cores?
  1. If your domain *doesn&#39;t* easily benefit from parallel computation, then explaining why is interesting, too.

Finally, I&#39;ve framed this as a multicore question, but feel free to talk about other types of parallel computing.  If you&#39;re porting part of your app to use [MapReduce][9], or if [MPI][10] on large clusters is the paradigm for you, then definitely mention that, too.

**Update:** If you do answer #5, mention whether you think things will change if there get to be more cores (100, 1000, etc) than you can feed with available memory bandwidth (seeing as how bandwidth is getting smaller and smaller per core).  Can you still use the remaining cores for your application?


  [1]: http://en.wikipedia.org/wiki/High-performance_computing
  [2]: http://www.gotw.ca/publications/concurrency-ddj.htm
  [3]: http://www.openmp.org/
  [4]: http://www.erlang.org/
  [5]: http://www.haskell.org/
  [6]: http://en.wikipedia.org/wiki/CUDA
  [7]: http://www.threadingbuildingblocks.org/
  [8]: http://upc.lbl.gov/
  [9]: http://labs.google.com/papers/mapreduce.html
  [10]: http://www.open-mpi.org/

How are you taking advantage of Multicore?

I&#39;ve been reading the &quot;Real World Haskell&quot; book, the chapter on concurrency and parallelism. My question is as follows:

- Since Haskell threads are really just multiple &quot;virtual&quot; threads inside one &quot;real&quot; OS-thread, does this mean that creating a lot of them (like 1000) will not have a drastic impact on performance? I.e., can we say that the overhead incurred from creating a Haskell thread with `forkIO` is (almost) negligible? Please bring pactical examples if possible.

- Doesn&#39;t the concept of lightweight threads prevent us from using the benefints of multicore architectures? As I understand, it is not possible for two Haskell threads to execute concurrently on two separate cores, because they are really one single thread from the operating system&#39;s point of view. Or does the Haskell runtime do some clever tricks to ensure that multiple CPU&#39;s can be made use of? 

Haskell lightweight threads overhead and use on multicores

I can understand how one can write a program that uses multiple processes or threads: fork() a new process and use IPC, or create multiple threads and use those sorts of communication mechanisms.

I also understand context switching. That is, with only once CPU, the operating system schedules time for each process (and there are tons of scheduling algorithms out there) and thereby we achieve running multiple processes simultaneously.

And now that we have multi-core processors (or multi-processor computers), we could have two processes running simultaneously on two separate cores.

My question is about the last scenario: how does the kernel control which core a process runs on? Which system calls (in Linux, or even Windows) schedule a process on a specific core?

The reason I&#39;m asking: I&#39;m working on a project for school where we are to explore a recent topic in computing - and I chose multi-core architectures. There seems to be a lot of material on how to program in that kind of environment (how to watch for deadlock or race conditions) but not much on controlling the individual cores themselves. I would love to be able to write a few demonstration programs and present some assembly instructions or C code to the effect of &quot;See, I am running an infinite loop on the 2nd core, look at the spike in CPU utilization for *that specific core*&quot;.

Any code examples? Or tutorials?

edit: For clarification - many people have said that this is the purpose of the OS, and that one should let the OS take care of this. I completely agree! But then what I&#39;m asking (or trying to get a feel for) is what the operating system actually does to do this. Not the scheduling algorithm, but more &quot;once a core is chosen, what instructions must be executed to have that core start fetching instructions?&quot;

How to control which core a process runs on?

I have a couple of small questions. 

Firstly is there a difference between multithreading and multicore? Are they two completely different things or does multithreading use more than one core if it needs? 

Secondly Most cores have two threads but when profiling my app I noticed lots of different threads ranging from thread 128 to thread 3460. What dictates how many threads your computer has?

Thanks

Multithreading and multicore differences

On a single core CPU, each process runs in the OS, and the CPU jumps around from one process to another to best utilize itself. A process can have many threads, in which case the CPU runs through these threads when it is running on the respective process.

Now, on a multiple core CPU:

- Do the cores run in every process together, or can the cores run separately in different processes at one particular point of time? For instance, you have program A running two threads. Can a dual core CPU run both threads of this program? I think the answer should be yes if we are using something like [OpenMP][1]. But while the cores are running in this OpenMP-embedded process, can one of the cores simply switch to other process?

- For programs that are created for single core, when running at 100%, why is the CPU utilization of each core distributed? (e.g. A dual core CPU of 80% and 20%. The utilization percentage of all cores always add up to 100% for this case.) Do the cores try to help each other by running each thread, of each process, in some ways?

  [1]: http://en.wikipedia.org/wiki/OpenMP

How do SMP cores, processes, and threads work together exactly?

I just got a new quad core computer and noticed that nmake is only using 1 process.

I used to use make which had the switch -j4 for launching 4 processes.  What is the nmake equivalent?


[edit]
Based on the information below I have been able to add a command to my qmake project file:

QMAKE_CXXFLAGS += /MP

Which effectively did it for me.  Many thanks.

How do I utilise all the cores for nmake?

I&#39;m confused about the notion of &quot;spark&quot; 

Is it a thread in Haskell? Or is the action of spawning a new thread ? 

Thanks everybody:

So to summarize, sparks are not thread but more of unit of computation (tasks to put it in C#/Java terms). So it&#39;s the Haskell way of implementing the task parallelism.

What is a &quot;spark&quot; in Haskell

I was very confused but the following thread cleared my doubts:

[Multiprocessing, Multithreading,HyperThreading, Multi-core][1]

But it addresses the queries from the hardware point of view. I want to know how these hardware features are mapped to software?

One thing that is obvious is that there is no difference between MultiProcessor(=Mutlicpu) and MultiCore other than that in multicore all cpus reside on one chip(die) where as in Multiprocessor all cpus are on their own chips &amp; connected together.

So, mutlicore/multiprocessor systems are capable of executing multiple processes (firefox,mediaplayer,googletalk) at the &quot;sametime&quot; (unlike context switching these processes on a single processor system) Right?

If it correct. I&#39;m clear so far. But the confusion arises when multithreading comes into picture. 

1. MultiThreading &quot;is for&quot; parallel processing. right?

2. What are elements that are involved in multithreading inside cpu? diagram? For me to exploit the power of parallel processing of two independent tasks, what should be the requriements of CPU?

3.   When people say context switching of threads. I don&#39;t really get it. because if its context switching of threads then its not parallel processing. the threads must be executed &quot;scrictly simultaneously&quot;. right?

 My notion of multithreading is that:
Considering a system with single cpu. when process is context switched to firefox. (suppose) each tab of firefox is a thread and all the threads are executing strictly at the same time. Not like one thread has executed for sometime then again another thread has taken until the context switch time is arrived.

4. What happens if I run a multithreaded software on a processor which can&#39;t handle threads? I mean how does the cpu handle such software?

5. If everything is good so far, now question is HOW MANY THREADS? It must be limited by hardware, I guess? If hardware can support only 2 threads and I start 10 threads in my process. How would cpu handle it? Pros/Cons? From software engineering point of view, while developing a software that will be used by the users in wide variety of systems, Then how would I decide should I go for multithreading? if so, how many threads?



  [1]: https://stackoverflow.com/questions/680684/multi-cpu-multi-core-and-hyper-thread

All Multicore Solutions on Gang of Coders

Total of 20 Multicore Solutions