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).

223 questions
1
vote
1 answer

Hyperthreading makes my code run slower?

Some multithreaded code I just wrote appears to run slower under hyperthreaded CPUs - i.e. disabling hyperthreading makes it run FASTER. Is this normal?
Optimizer
  • 11
  • 2
1
vote
1 answer

Number of cores to speedup calculation

I'm trying to calculate speedup of a code using Amdahl's law and the following are my CPU specs: Amdahl's law:- Speedup = 1 / 1-p+ (p/n) where n = number of processors. According to my specs, it says cores = 4 while logical processors = 8 What…
S.Dan
  • 1,826
  • 5
  • 28
  • 55
1
vote
0 answers

Can I disable Hyper Threading by setting processor affinity?

I am developing on an Intel I7-6700 (4 cores, 8 logical HT processors) . Can I safely assume, if I set processor affinity to 1 processor (out of the 8 logical processor) , that Hyper Threading will never ever happen? Unfortunately, I am unable to…
Gary
  • 99
  • 2
  • 10
1
vote
0 answers

Hyper Threading OFF on PREEMPT RT Kernel 3.10.103-rt114

I have a Kernel compilation related issue where after successfull compilation and reboot HyperThreading option is lost. I am trying to update my Cent OS 7 vanilla kernel with PREEMPT RT kernel. This is my first trial or experiment with Kernel. The…
1
vote
0 answers

Disable hyper-threading for better Solr performance?

I have a machine with 16 real cores (32 with HT enabled). I'm running on it a Solr server and trying to reach maximum performance for indexing and queries (indexing 20k documents/sec by a number of threads). I've read on multiple places that in some…
Avner Levy
  • 6,601
  • 9
  • 53
  • 92
1
vote
1 answer

Using matlabpool with a specified number of workers

I've been using the command matlabpool open 8 for a while in order to speed up things. However I just tried using it and am denied 8 cores and now limited to 4. My laptop is an i7 with 4 cores but hyperthreaded which meant I had no issue making…
1
vote
1 answer

Kernel Threads vs Hyperthreads

What is the difference between kernel threads and hyper-threads? Or they are same? I understand that it the kernel threads that os schedules not the user threads. Seen nobody talking about both of them same time......
1
vote
1 answer

Windows phone emulator in windows 8.1 pro (64-bit)

I am trying to enable hyper thread on my pc windows 8.1 pro (64-bit). It is core i3 h61m-ds2 gigabyte motherboard. I have installed coreinfo.exe from there i have seen that my pc have hyper thread facility. I follow all the step describe here :…
Developer
  • 385
  • 1
  • 3
  • 18
1
vote
3 answers

Multithreaded(Hyperthreading) v/s multicore processors

I am doing a parallel computing course at my university and apparently we need to know the architectures at programmer's level. Can anyone tell what is the motivation for developing multicore processors? Why multithreaded processors won't suffice?…
ishan3243
  • 1,870
  • 4
  • 30
  • 49
1
vote
2 answers

CPU time on multicored/hyperthreaded

I need to observe the CPU time took by a process in a multicored/hyper-threaded. Suppose a Xeon, Opteron, etc. Let's assume I have 4 cores, hyper threaded, meaning 8 'virtual' cores. Let X the program I want to run an observed how much CPU time it…
hectorpal
  • 711
  • 2
  • 6
  • 15
1
vote
1 answer

Hyperthreading on Mac -- not giving much speed up

I have implemented a Convex hull algorithm in C++ using openMP. The code can be found here: http://codepad.org/VVQdSdfM Below are the results when tested in my Mac Book Pro: Processor Name: Intel Core i5 Processor Speed: 2.5 GHz …
1
vote
2 answers

Is CPU time relevant to Hyperthreading?

Is increased CPU time (as reported by time CLI command) indicative of inefficiency when hyperthreading is used (e.g. time spent in spinlocks or cache misses) or is it possible that the CPU time is inflated by the odd nature of HT? (e.g. real cores…
Kornel
  • 97,764
  • 37
  • 219
  • 309
1
vote
1 answer

Intel IPP library requirements

So I am trying to compile an Intel IPP sample application that comes with the library -- string matching --, and I don't seem be able to leverage the IPP instructions. The computational time stays the same when I disable one of the cores on my…
SMir
  • 650
  • 1
  • 7
  • 19
1
vote
1 answer

Disable Hyperthreading in Mac-pro 2008 from EFI?

Is there a way of disabling HT at a firmware level (EFI) ?? I have a server-linux distribution and a macosx both installed in a mac-pro 2008 workstation. Searching in google, i came up with the EFI shell command 'cpuconfig threads off' but this only…
labotsirc
  • 722
  • 7
  • 21
0
votes
2 answers

Can hyperthreading affect atomicity of 32-bit int read/write on a 32-bit processor?

I have read somewhere that hyperthreading can make 32-bit int (on a 32-bit processor) read and write non-atomic even when it is boundary aligned. Can anyone explain how hyperthreading effects this?
sachin
  • 1,141
  • 2
  • 16
  • 21