hyperthreading Questions

16

Solved

I'm building a PC with the new Intel I7 quad core processor. With hyperthreading turned on it will report 8 cores in Task Manager. Some of my colleagues are saying that hyperthreading will make th...
Hydrogeology asked 20/1, 2009 at 18:44

3

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Two different threads within a single process can share a common memory location by reading and/or writing to it. Usually, such (intentional) sharing is implemented using atomic operations using ...
Shied asked 10/8, 2017 at 0:37

1

I read that the multithreading is the feature that a single core can manage many threads (not in parallel) and the benefit is that the CPU is always working. For the Hyperthreading that a single co...

4

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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 s...
Assiniboine asked 25/3, 2009 at 8:32

4

I found references to hart on page 35 of the RISC-V 2.1 spec. However, I could not find a definition for hart in this document. Does hart refer to a hardware-thread or something more sinister?
Garibald asked 8/3, 2017 at 16:33

2

While debugging some performance issue in app I'm working on, I found out weird behaviour of kernel scheduler. It seems that busy SCHED_FIFO tasks tend to be scheduled on logical cores from the sam...
Selfinterest asked 7/4, 2022 at 14:40

4

I am using the Ubuntu. How can I check whether Hyper Threading is enabled or not. And if it is disabled, how can I enable it?
Pragmatics asked 13/4, 2015 at 12:25

5

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How do I assign 2 MPI processes per core? For example, if I do mpirun -np 4 ./application then it should use 2 physical cores to run 4 MPI processes (2 processes per core). I am using Open MPI 1.6...
Queue asked 31/7, 2012 at 21:20

5

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The primary idea behind HT/SMT was that when one thread stalls, another thread on the same core can co-opt the rest of that core's idle time and run with it, transparently. In 2013 Intel dropped...
Cattalo asked 15/4, 2014 at 8:48

1

I’m using a project where each time you double the number of threads, you add between 40% to 60% overhead. As hyperthreading increases performance to a maximum of 30% this means, the program runs s...
Kaufman asked 28/4, 2020 at 15:12

3

I'm a student doing some research on Hyper-threading recently. I'm a little confused about the feature - L1 Data Cache Context Mode. In the architecture optimization manual, it was described that ...
Earsplitting asked 3/9, 2012 at 14:36

5

This is a tough one. I need to use a command to output the exact number of cores from my servers. My tests: X: On a Windows server with 4 processors (sockets) and 2 cores each without HT. Y: O...
Massimiliano asked 1/9, 2016 at 14:30

0

I want to detect the number of real physical cores, not logical cores, for workloads that scale negatively when more threads compete for private per-core caches, and/or have high enough IPC that ru...
Undergarment asked 19/3, 2020 at 10:37

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I have a number of Java processes using OpenJDK 11 running on Windows Server 2019. The server has two physical processors and 36 total cores; it is an HP machine. When I start my processes, I see w...
Ignition asked 16/1, 2020 at 20:28

14

I have a multi threaded c++ application that runs on Windows, Mac and a few Linux flavors. To make a long story short: In order for it to run at maximum efficiency, I have to be able to instantia...
Ultrasound asked 25/5, 2010 at 2:57

6

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I spent this morning trying to find out how to determine which processor id is the hyper-threaded core, but without luck. I wish to find out this information and use set_affinity() to bind a proc...
Baffle asked 1/9, 2011 at 18:12

1

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I have an Intel CPU with 4 HT cores (8 logical CPUs) and I built two simple processes. The first one: int main() { for(int i=0;i<1000000;++i) for(int j=0;j<100000;++j); } The second one...
Filippa asked 25/9, 2019 at 20:59

1

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Can different processes run RDTSC at the same time? Or is this a resource that only one core can operate on at the same time? TSC is in every core (at least you can adjust it separately for every c...
Snowblind asked 4/6, 2019 at 8:2

1

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Imagine a CPU (or core) that is superscalar (multiple execution units) and also has hyperthreading (SMT) support. Why is the number of software threads the CPU can truly execute in parallel typica...
Amritsar asked 11/4, 2019 at 15:48

3

Can two processes simultaneously run on one CPU core, which has hyper threading? I learn from the Internet. But, I do not see a clear straight answer. Edit: Thanks for discussion and sharing! My...
Nubile asked 18/1, 2012 at 20:10

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I would like to know the optimal number of threads I can run. Normally, this equals to Runtime.getRuntime().availableProcessors(). However, the returned number is twice as high on a CPU supportin...
Sylvestersylvia asked 31/7, 2012 at 10:31

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To my knowledge, both MMU and TLB are not shared in a hyper-threaded core in Intel x86_64. However, then, if two threads that don't share the address space are scheduled to the same physical core,...
Serow asked 16/7, 2018 at 11:31

1

Can anyone confirm that for example Intel i3 CPU has 2 physical cores and 4 logical cores, so if I set Process affinity to Core #0 so that means I set on first physical cores 1 logical core, but if...
Festal asked 29/5, 2018 at 8:41

1

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I'm having a hard time understanding hyper-threading. If the logical core doesn't actually exist, what's the point of using hyper-threading?. The wikipedia article states that: For each processo...
Derrickderriey asked 23/11, 2017 at 2:38

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I was wondering if someone could explain me the difference b/w these two ? Has it something to do with intel hardware architecture (HT) ?
Consonance asked 3/1, 2013 at 16:49

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