Unix and Linux Stack Exchange
Unix and Linux Stack Exchange

Questions tagged [hyperthreading]

27 questions
79
votes
15 answers

Checking if HyperThreading is enabled or not?

How can I check if hyperthreading is enabled on a Linux machine, using a perl script to check for it? I'm trying the following way: dmidecode -t processor | grep HTT Let me know if I'm on right track.
doubledecker
  • 1,807
  • 3
  • 15
  • 12
53
votes
3 answers

VirtualBox: Is it a bad idea to assign more virtual CPU cores than number of physical CPU cores

VirtualBox: As I have Hyper-Threading capable CPU, I wonder: Is it a bad idea to assign more virtual CPU cores than a number of physical CPU cores as the following warning suggests (simply using all 8 virtual cores of 4 physical core CPU for…
Vlastimil Burián
  • 27,586
  • 56
  • 179
  • 309
13
votes
3 answers

How can I have 400% CPU occupied on 2 cores

I understand that Σ(%CPU) ≤ logicalcores*(1+ε) (where ε is measure and rounding error). But, how can I have on a 2 core system 2 different processes, each taking 200% of CPU (as measured by htop)? EDIT Cores in above equation means logical cores…
Maciej Piechotka
  • 16,578
  • 11
  • 57
  • 93
11
votes
1 answer

What does "cpu MHz" field mean in the /proc/cpuinfo of a hyper-threading cpu?

The CPU is a [email protected]. It has 4 cores and each core has 2 threads. Here is the dmidecode output: # dmidecode -t 4 # dmidecode 2.9 SMBIOS 2.7 present. Handle 0x0042, DMI type 4, 42 bytes Processor Information Socket Designation: SOCKET 0 …
Chris Tsui
  • 263
  • 1
  • 2
  • 9
6
votes
1 answer

Should I disable hyperthreading when concerned about performance of single-threaded applications?

I use a i5-2410M processor, which is setup to do hyperthreading by default on my laptop. Considering that this is a 2-core processor, this means it can do 4 threads at a time. This also means that single-threaded applications only use a maximum of…
tshepang
  • 64,472
  • 86
  • 223
  • 290
4
votes
1 answer

Can hyperthread be enabled

I would like to know if hyperthread can be enabled on my operating system or not? I am using HP-UX Itanium, below is truncated output of machinfo Intel(R) Itanium(R) Processor 9560 (2.53 GHz, 32 MB) 8 cores, 16 logical processors per socket …
Learning_DBAdmin
  • 159
  • 6
4
votes
1 answer

Unexpected processor/core counts for AMD processor

I wanted to determine if a machine has hyperthreading enabled or not. To determine this, I used advice I found online, which operates as follows: physical_proc_count = `grep "physical id" /proc/cpuinfo | sort -u | wc -l` logical_proc_count = `grep…
CptSupermrkt
  • 1,492
  • 5
  • 16
  • 26
3
votes
2 answers

Why does higher CPU-usage slow down a task?

I am using whisper.cpp to transcribe some sound files. It is a very CPU heavy process so I try to find some optimal settings and therefore I have done some tests with the thread setting (-t) but the results are super confusing. This is the command I…
d-b
  • 1,703
  • 2
  • 17
  • 26
3
votes
0 answers

How do I flag a process to avoid hyperthreading (SMT)?

Suppose I have an 18 core CPU with SMT enabled, and there are 18 long runnning processes, all using ~100% of a thread. If I start a 19th process, the kernel will schedule it to run on one of the cores, as a hypersibling of one of the 18 other…
uLoop
  • 141
  • 2
3
votes
1 answer

How to reliably tell from Linux whether the CPU supports Hyperthreading, even if Hyperthreading is disabled?

The following is what I am doing to tell whether a processor does support HT or not, regardless of whether it is enabled or disabled: # dmidecode -t processor | grep "Hardware Thread" | wc -l If result is 0, then the processor does not support…
Raulinbonn
  • 66
  • 7
3
votes
1 answer

CMOS occasionally resets hyperthreading. Can I force hyperthreading on using Linux kernel?

I have some i7-4700EQ based embedded server systems that require hyperthreading. All is good except that, on rare occasions, the hyperthreading flag in CMOS gets set to disabled. While the hardware is still in my possession, I can simply reboot,…
Hugh McCurdy
  • 53
  • 5
3
votes
1 answer

Hyper Threading and Process Priority

Are there any methods (linux kernel options, sysctl settings or configurable scheduler modules) that can cause a high priority process/thread to run on a physical processor core with the second (hyper threading) virtual core unscheduled in order to…
Juergen
  • 508
  • 4
  • 13
3
votes
1 answer

Hyperthread and processors Clock, Size, and Capacity

When I enable hyperthreading, CPU size and capacity decrease to about half the non-hyperthreaded value. Since most of my processes use only two cores, should I disable hyperthreading? lshw -C processor (cpu:0 and cpu:1 show the same…
Raphael Calmon
  • 31
  • 2
2
votes
2 answers

How hyperthreading is useful in kvm based guest VM?

We are creating virtual os threads inside guest os but the actual physical core is on the host machine. Will hyperthread = true in guest VM config make any difference? I can visualize how hyperthreading works on the host as it has a physical core,…
Karthik Nedunchezhiyan
  • 737
  • 9
  • 22
2
votes
2 answers

Hyperthreading not detected by Linux

I have a Dell server with two Intel Xeon E5645 cpus, each cpu has 6 cores, and each core is hyperthreaded (i.e. should be equivalent to two virtual cores). I installed CentOS 6.2 on this server and it seems to detect only 12 cores (although there…
Oren Mel
  • 29
  • 1
  • 3
1
2