235 questions
-1
votes
1
answer
59
views
Multi Processing vs Multi Threading and Hyper-Threading
What is the difference between thread and process? Threads can use multi core and process use multi core too. Threads shares same memory but process cant share. What if we use shared memory for multi-...
1
vote
2
answers
66
views
Hyperthreading: SIMD and scalar execution at the same time. Is it possible? [closed]
I have a question regarding cpu execution. A CPU can hyperthread, by letting different processes use different components of the cpu at the same clock cycle. But I wonder if this can be used to speed ...
1
vote
1
answer
442
views
Hyper Threading: nosmt in grub configuration
Currently, I have running Debian 12 instance on dedicate CPU cloud environment. It has 2 cores, 4 threads.
It is not impossible to turn off hyper threading via BIOS settings.
I found possibility to ...
- 183
0
votes
0
answers
110
views
mpi4py There are not enough slots available in the system
I am using mpi4py, and submit a job to Slurm where I have the following specification:
#!/bin/bash
#SBATCH -N 2
#SBATCH --ntasks-per-core=2
module load --auto python/3.9.15-gcc-12.2.0-3sr5utz
module ...
- 231
0
votes
2
answers
163
views
Why do two logical cores belonging to the same physical core have different frequencies?
When enabling Turbo mode on the CPU, the operating frequency fluctuates with changes of the workload. I observed through the turbostat command that each core has a different frequency during operation....
- 591
2
votes
0
answers
246
views
Simultaneous multi threading in RISCV
In RISCV architecture, does simultaneous multi threading allow threads of two different privilege modes run simultaneously sharing the processor's issue width?
Can OS and application programs share ...
- 121
0
votes
1
answer
630
views
What's the impact of hyperthreading on low-latency development
I've read a post regarding low-latency development as below.
"We always avoid (relatively) slow language features like exceptions, memory allocation and virtual function calls on the critical ...
- 11
1
vote
1
answer
151
views
How to judge if a given workload is hyper-thread friendly?
How do I tell if a certain working set is suitable for hyper-threading, other than just turning the hyper-threading option on/off and doing a direct performance test?
There are two main problems:
Can ...
- 591
0
votes
0
answers
284
views
Does hyperthreading have an bad impact on a core which is fully occupied
I have been learning for an exam and try to understand hyperthreading.
Lets suppose we have a physical core with hyperthreading, Thread A and B. Let's also suppose thread A has fully occupied the ...
- 1
2
votes
1
answer
248
views
Does simultaneous multithreading make use of interleaved / temporal multithreading?
I am trying to understand simultaneous multithreading (SMT) but I have just run into a problem.
Here is what I figured out so far
SMT requires a superscalar processor to work. Both technologies - ...
- 21
0
votes
0
answers
285
views
Why does hyperthreading not improve web worker performance, and why does navigator.hardwareConcurrency not take this into account?
Multiple StackOverflow answers say that the optimal number of web workers to use is equal to the number of physical cores in the machine, not the number of logical cores. This matches my personal ...
- 338
1
vote
1
answer
388
views
Running Slurm array jobs one per virtual core instead of one per physical core
we have a machine with 2x64-core CPU, each core consists of 2 virtual cores, so in htop we see 256 distinct (virtual) CPUs. We configured Slurm quality of service to better manage CPU usage per user. ...
- 658
0
votes
1
answer
59
views
Hyperthread consumes more CPU for same work compared to CPU consumed while hyperthread is disabled
I have 2 core machine with hyperthreading enabled, so I have 4vCPUs(0,1,2,3). There are several threads running which are pinned to vCPU 1 and 3. So that hyperthreads are not used. Now I have this ...
- 41
0
votes
2
answers
6k
views
What does it mean when we say "4 cores 8 threads"? [closed]
When I run lscpu on my host, it shows
CPU(s): 8
Thread(s) per core: 2
Core(s) per socket: 4
My host has 4 physical CPUs, but 8 logical CPUs due to 2 threads per core. ok, "2 ...
- 8,748
2
votes
2
answers
419
views
Does Visual Studio build time benefit much from hyperthreading?
I'm looking at getting an i7-3770 to replace my i5-2500K in my aged 1155 LGA based PC. Clock speeds are quite similar, and Ivy Bridge was a fairly small improvement over Sandy Bridge ...
- 404
2
votes
1
answer
9k
views
What is the difference between Hyperthreading and Multithreading? Does AMD Zen use either?
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 core ...
2
votes
1
answer
198
views
Can hardware threads access main memory at the same time?
I am trying to understand microarchitecture.
When an operating system schedules code to run on a CPU hardware thread (as in Intel HyperThreading), can each execution context issue memory reads in ...
- 161
0
votes
0
answers
489
views
Local Memory vs Global Memory
Just for clarity.
Does Local Memory refer to the memory allocated to a certain program?
And does the Global memory refer the the Main memory?
I am reading about Uniform Memory Access time and Non ...
- 370
1
vote
0
answers
81
views
Why application runs faster when co-located with another app on a logical core?
I have two applications (both with a single thread). One is a word reindexing application (named wrmem) which could be found here, and the other one is a simple loop that iterates over an array.
I ...
- 1,242
2
votes
0
answers
509
views
Control threads inside oneAPI/MKL/BLAS/cblas_dgemm(and cblas_daxpy) for different multi-threaded schemes
I'm measuring the time-performance of multiple multi-threaded schemes nested with BLAS functions. More specifically, the following calls:
cblas_dgemm(CblasColMajor, CblasTrans, CblasNoTrans,
phr, phr,...
- 51
3
votes
1
answer
526
views
Sharing a TLB entry between two logical CPUs (Intel)
I wondered if it is possible if two threads belonging to the same program with the same PCID can share the TLB entry when they are scheduled to run on the same physical CPU?
I already looked into the ...
0
votes
0
answers
20
views
[risc-v]does 2-way Simultaneous multithreading core share register files, or do they have separate registers? [duplicate]
For example, in an 4-core system with 2-way SMT, you have 8 harts, which is it? 4 separate x0-x31 registers ,pc, and csrs, or 8 separate x0-x31, pc, and csrs?
- 121
6
votes
2
answers
722
views
Why SCHED_FIFO threads are assigned to the same physical CPU even though idle CPUs are available?
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 same ...
- 35
0
votes
2
answers
4k
views
Kubernetes CPU allocation: is vCore vs vCPU vs core in Azure?
I am running a Java application on an Azure Kubernetes node with a Standard_D8s_v3 VM. I am unsure about CPU allocation for a kubernetes deployment. This mentions that 1 CPU is equals to 1 Azure vCore....
0
votes
0
answers
107
views
How do get this function to run on multiple cores/processors in R?
How would I go about running this function across multiple cores on my machine to speed it up. The function implements a backfitting algorithm to fit a nonparametric bivariate linear model using ...
2
votes
0
answers
280
views
strange CPU binding/pining result within OpenMPI
I have tried to evaluate an OpenMPI program with Matrix Multiplication algorithm, the written code scales very well on a single thread per core machine in our Laboratory (close to ideal speedup within ...
- 137
1
vote
1
answer
726
views
Is Simultaneous Multithreading (Hyperthreading) "true" multicore processing?
So what I am aware of is that Simultaneous Multithreading (Intel's Hyperthreading for example) enables a single CPU core to efficiently manage several threads at once. And most explainations I find is ...
- 57
0
votes
0
answers
1k
views
Best thread to core ratio for hyperthreading processors
I did some research and I came to the conclusion that 1 thread per core is the best performing ratio, but the questions I read referred to very old cpus which had 2 cores and 2 threads. For a ryzen ...
- 329
0
votes
2
answers
332
views
Best way to compute a big Mandelbrot image
I try to calculate a fractal image, and as the calculation could be long as the resolution increase, I was wondering if I could use Hyper Threading to calculate "tiles" of my final image and ...
- 11
0
votes
0
answers
439
views
Why is executing two threads on two logical cores better than executing two threads on one physical core?
Modern CPU specifications seem to always mention twice the number of threads for each core. If it is a 4-core processor, the number of threads mentioned is 8. If it is a 6-core processor, the number ...
- 11
2
votes
0
answers
202
views
Atomic operation contention between SMT/HT Threads
Across modern AMD/Intel CPU's is contention for atomics (inc/dec/swap etc) between say 2 SMT/HT threads on the same core known to have significantly better performance in general than between threads ...
- 1,713
1
vote
1
answer
259
views
Is synchronization faster on the same physical CPU core?
I have a question. If a thread modifies a variable, will the thread on the same physical core (a different hyperthread core) see the modification earlier than other cores? Or it has to wait until all ...
0
votes
1
answer
155
views
What problems Hyperthreading can solve?
Sorry for being stupid but recently I stamped upon Hyperthreading and I was amazed how epic and awesome it is but I was wondering what problems it can fix.
- 21
1
vote
2
answers
880
views
Why does my pc prefer even numbered cores?
My pc has a 10th gen Core i7 vPRO with virtualization enabled. 8 cores + 8 virtual cores. (i7-10875H, Comet Lake)
Each physical core is split into pairs, so Core 1 hosts virtual cores 0 & 1, core ...
- 1,277
1
vote
1
answer
398
views
How to test performance of Intel HyperThreading in Linux X86_64 [closed]
I am trying to figure out the performance impact of Intel HT in Linux X86_64.
Is there a well know tool or ready-to-use code to do this testing ?
If not, my test plan is as follows,
Scenario 1:
Thread ...
- 1,163
2
votes
0
answers
340
views
How does Hyper-Threading affect the cache?
When I was using Hyper-Threading, a very strange phenomenon appeared. I was using c language to measure the time of l2 hit. I wrote the test time in a program A. When I run it alone, it showed that it ...
- 776
0
votes
0
answers
412
views
Relation between cpu, multi-processor and multi-core; how many cores my computer has [duplicate]
My OS is Ubuntu 18.04, my computer cpu is Intel(R) Core(TM) i7-8700 CPU @ 3.20GHz
When I use cat /proc/cpuinfo, I find my cpu has 12 (processor 1 - 11) processors. Every processor has info as below, ...
- 309
0
votes
0
answers
37
views
Single Windows process cannot use all of the 80 available threads of my setup, why?
I have both Linux and Windows 10 installed on a dual Xeon 6138 computer with 64GB of RAM.
I cannot access the computer immediately (because of the lockdown) but I strongly believe the Windows version ...
- 309
-3
votes
1
answer
1k
views
How to verify if your processor supports hyper-threading?
This is my first post on StackOverflow so I apologize if I have broken some rules.
My Professor, (not a great one) has just told us we have 24 hours to write a program under 10 lines of code that ...
0
votes
0
answers
51
views
threads and intel's (and AMD's) product descriptions [duplicate]
Many years ago ago I created many-threaded code on one-kernel processors. I don't remember if it was Posix' PThreads.
Can someone please clarify what Intel/AMD means when they say "4 cores 4 ...
0
votes
3
answers
2k
views
Are threads run on CPU or core?
Is a single thread run on a single core or a single CPU?
Also, I have i7. It says I have 4 cores, but 8 threads. Isn't core related with thread in 1-1 proportion? How did it double it?
- 521
0
votes
1
answer
673
views
Disabling Hyperthreading on Nodes in an AWS EC2 Cluster through Ray Configuration
I have a task running on an EC2 cluster which starts to slow down progressively as virtual CPUs are employed (regardless of EBS volume size). To avoid this I want to disable hyperthreading on all ...
- 145
1
vote
1
answer
1k
views
Should I aim for multiple physical cores or multiple threads for parallel computing in R?
I am new to parallel computing and this may be a trivial question. I am thinking about which processor to choose for parallel computing (on a single machine)? In particular, I would like to know ...
- 13
1
vote
0
answers
1k
views
Can't find WSL kernel directory not in /usr/src and not in /lib/modules
I am not a developer, and don't have enough experience with Linux.
I am a data scientist and wants to know how to improve my performance using my CPUs better.
I have a linux VM with 2 physical CPUs, ...
- 41
3
votes
1
answer
342
views
How to bind a process to only physical cores in a cross system way?
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 ...
- 3,052
1
vote
0
answers
1k
views
Does Hyper Threading will decrease the performance of Docker?
I have the below configuration server, In this we are running only Docker, All the applications are running as Docker container , Expect Docker , no other application are installed in the OS
System ...
- 147
7
votes
1
answer
2k
views
How to find the Number of physical CPU Cores (not logical SMT hyperthreads) via .NET Core?
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 ...
- 101
1
vote
0
answers
879
views
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 ...
2
votes
0
answers
121
views
With SMT, what do we call a "hardware thread"?
These days we have a CPU which may comprise several Cores, and each Core may support SMT... so when the OS allocates a "processing resource" to a (software) thread (so that it can run), the question ...
- 1,752
7
votes
0
answers
561
views
JVM only using half the cores on a server
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 ...
- 595