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Questions tagged [hyperthreading]

In a hyperthreaded CPU, for each processor core that is physically present, the operating system addresses two virtual or logical cores, and shares the workload between them when possible.

In an hyper threaded environment, For each processor core that is physically present, the operating system addresses two virtual or logical cores, and shares the workload between them when possible.

This allows to decrease the number of dependent instructions on the pipeline. It takes advantage of superscalar architecture (multiple instructions operating on separate data in parallel).

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How to write to CSV asynchronously

I have to test about one million possible urls. If the url is valid I want to store it in a CSV. To speed things up I want to use asynchronously. Code works fine when ran with a for loop, but the CSV is empty if I run it asynchronously. …
Lev
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available threads in Knights Landing

I am programming on a Knights Landing node which has 68 cores and 4 hyperthreads/core. I am working on a hybrid MPI/OpenMP application. My question is if the 4 hyperthreads are meant to be used as OpenMP threads or how could I use them? When I run…
armando
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How to detect multicore scalability/contention issues

I'am facing a scalability issue on multicore system. My application is processing scientific data in parallel on a 4 physical core machine, 8 logical cores with hyperthreading activated. We launch 8 JVM, one per logical core (we'll probably switch…
greg
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disabling interrupts on hyperthreaded processor

Let say I have a hyper-threaded processor and OS sees them as two different virtual processors vp1 and vp2. Now in an LWP1 on vp1, I disable hardware interrupt interrupts. Does not it amounts to say that both of the virtual processors wont get any…
ultimate cause
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Measuring performance impact of hyperthreading

On Intel systems, how would I measure CPU cache misses and pipeline stalls and use them in a formula to determine if hyperthreading should be on or off for my workload? I have benchmarked and reliably get a 12% improvement with HT on but I want to…
Gaius
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Can the two threads of a virtual core (hyperthreading) be running different OS processes?

I found the following quotation from another answer (Performance difference for multi-thread and multi-process): Next, you can have CPUs with "hyperthreading", which can run (at least) two threads on a core very rapidly -- but, not processes…
Harris M Snyder
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Strange speedup with OpenMP

I have some strange results while testing OpenMP. As a test case, I sum two vectors of floats, a problem which should perfectly parallelizable. For vectors large enough on my quad-core CPU with Hyper-threading, which essentially means that I should…
Alexander Shamanskiy
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Testing on a single-core PC with hyperthreading

If a multithreaded program runs safe on a single-core CPU with hyperthreading, will it also run safe on a dual-core CPU with hyperthreading? Concerning thread-safety etc. EDIT Ok, I try to be more specific. I mean the bad source code lines, where I…
Karl
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multiple parallel threads in java dont terminate

i try to run a set of parallel thread in java. im creating these through a high order function as follows: public static void parallelizedMap(Consumer f, List list, int count) { List> parts = new…
caesar
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Hyper Threads, SIPI and Registers

I'm interested to learn more regarding the x86 architecture, and how it implements multi-processing. Let's say using cpuid instruction you can recognize how many logical cores your processor has, and using some SIPI (Startup Inter Processor…
DrPrItay
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Can there be a race between two hyperthreads on the same CPU?

I am trying to avoid race conditions in my code, and I am currently working with a single hyperthreaded CPU, so there are two logical CPUs, each with their own thread. If my understanding of hyperthreading is correct, these threads share the same…
Alexander Bolinsky
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Hyper threading in hardware level

So, this semester I have a subject about operating systems, and I don't understand so much yet about Hyper threading. I searched internet but what I found are almost the same things (I don't know if I searched with the wrong terms). Here are the…
Gabriel Castro Fernandes
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How to decide whether to use hyperthreading or not?

Hyperthreading can hurt performance of some applications and it should not be used. From the Microsoft website (https://msdn.microsoft.com/en-us/library/cc615012%28BTS.10%29.aspx): It is critical hyper-threading be turned off for BizTalk Server …
Maciej
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When I'm testing about multiprocessing and threading with python, and I meet a odd situation

I am using process pools(including 3 processes). In every process, I have set (created) some threads by using the thread classes to speed handle something. At first, everything was OK. But when I wanted to change some variable in a thread, I met an…
xina1i
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how basic instructions run in parallel

Maybe this is a stupid question but I am trying to gain a better understanding of hardware inner workings... if a cpu has multi threads and we have a group of instruction set to assign it. as i read how it work from…
Akash Chaudhary
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