Use all cores linux

How do I make a multi-threaded app use all the cores on Ubuntu under VMWare?

I have got a multi-threaded app that process a very large data file. Works great on Window 7, the code is all C++, uses the pthreads library for cross-platform multi-threading. When I run it under Windows on my Intel i3 — Task manager shows all four cores pegged to the limit, which is what I want. Compiled the same code using g++ Ubuntu/VMWare workstation — same number of threads are launched, but all threads are running on one core (as far as I can tell — Task Manager only shows one core busy). I’m going to dive into the pThreads calls — perhaps I missed some default setting — but if anybody has any idea, I’d like to hear them, and I can give more info — Update: I did setup VMWare to see all four cores and /proc/cpuinfo shows 4 cores Update 2 — just wrote a simple app to show the problem — maybe it’s VMWare only? — any Linux natives out there want to try and see if this actually loads down multiple cores? To run this on Windows you will need the pThread library — easily downloadable. And if anyone can suggest something more cpu intensive than printf- go ahead!

#ifdef _WIN32 #include "stdafx.h" #endif #include "stdio.h" #include "stdlib.h" #include "pthread.h" void *Process(void *data) < long for (int i=0;i<100000;i++) < printf("Process %ld says Hello World\n",id); >return NULL; > #ifdef _WIN32 int _tmain(int argc, _TCHAR* argv[]) #else int main(int argc, char* argv[]) #endif < int numCores = 1; if (argc>1) numCores = strtol(&argv[1][2],NULL,10); pthread_t *thread_ids = (pthread_t *)malloc(numCores*sizeof(pthread_t)); for (int i=0;i for (int i=0;i return 0; > 

1 Answer 1

I changed your code a bit. I changed numCores = strtol(&argv[1][2], NULL, 10); to numCores = strtol(&argv[1][0], NULL, 10); to make it work under Linux by calling ./core 4 maybe you where passing something in front of the number of cores, or because type _TCHAR is 3byte per char? Not that familiar with windows.. Further more since I wasn’t able to stress the CPU with only printf I also changed Process a bit.

void *Process(void *data) < long hdata = (long)data; long for (int i=0;i<10000000;i++) < printf("Process %ld says Hello World\n",id); for (int j = 0; j < 100000; j++) < hdata *= j; hdata *= j; hdata *= j; hdata *= j; hdata *= j; hdata *= j; hdata *= j; hdata *= j; hdata *= j; hdata *= j; hdata *= j; . >> return (void*)hdata; > 

And now when I run gcc -O2 -lpthread -std=gnu99 core.c -o core && ./core 4 You can see that all 4 threads are running on 4 different cores well probably the are swapped from core to core at a time but all 4 cores are working overtime.

core.c: In function ‘main’: core.c:75:50: warning: cast to pointer from integer of different size [-Wint-to-pointer- cast] Starting 4 threads Process 0 says Hello World Process 1 says Hello World Process 3 says Hello World Process 2 says Hello World 

I verified it with htop hope it helps.. 🙂 I run dedicated Debian SID x86_64 with 4cores in case you’re wondering.

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How To All Cpu Cores To Max Proformance Ubuntu

There is a command or an extension “-j” which is used to specify the number of cores you want to use to execute a command. So, for example, if you have an Intel i7 processor, which has 4 cores, you can just add “-j4” at the end of your command and it will be executed using all four cores.

How do I set Ubuntu to high performance?

These Ubuntu speed up tips cover some obvious steps such as installing more RAM, as well as more obscure ones like resizing your machine’s swap space. Restart your computer. Keep Ubuntu updated. Use lightweight desktop alternatives. Use an SSD. Upgrade your RAM. Monitor startup apps. Increase Swap space. Install Preload.

How many cores can Ubuntu use?

The Ubuntu kernel is configured to support 8 processors / cores in 32-bit and 64 processors / cores in 64-bit.

How do I limit CPU cores in Linux?

To specify the number of CPU cores present on the system, use the –cpu or -c flag (this is normally detected automatically). Rather than limit a process’s CPU usage, we can kill it with the –kill or -k option.

Does Ubuntu use all cores?

Ubuntu uses the Linux kernel which makes use of symmetric multiprocessing (SMP) and multiple cores. It scales very well from low-end single-cpu single-core systems to high-end supercomputer clusters with thousands of multi-core CPUs.

How do I change my CPU governor in Ubuntu?

In /etc/init. d/ondemand change the line: echo -n $GOVERNOR > $CPUFREQ to: echo -n “performance” > $CPUFREQ if you decide to keep /etc/init.

How can I make Ubuntu 20.04 faster?

Tips to make Ubuntu faster: Reduce the default grub load time: Manage startup applications: Install preload to speed up application load time: Choose the best mirror for software updates: Use apt-fast instead of apt-get for a speedy update: Remove language related ign from apt-get update: Reduce overheating:.

How much RAM does Ubuntu have?

Open System Info. This can be done either in the dash, or by going to the gear icon (top right), opening System Settings, and opening System Info. Under the Ubuntu Logo and Version Number, it will state Memory 5.5GiB.

How many CPUs can Linux support?

The x86_64 Linux kernel can handle a maximum of 4096 Processor threads in a single system image. This means that with hyper threading enabled, the maximum number of processor cores is 2048.

Does Ubuntu support multiple processors?

Yes, Ubuntu is more than capable of using the Xeon PC you want to buy and detect all CPUs (Physical and Threads). It can also detect, as far as I have tested 4 sockets (4 CPUs) but the kernel version that Ubuntu uses can detect even more.

How can I get high performance?

7 ways to achieve consistently high performance Get physical for productivity. Let’s start with your physical well-being. Achieve a balanced life. Being a workaholic won’t help you perform at the highest level. Massage your mindset. Form the productivity habit. Plan for success. Be motivated. Don’t settle.

How do I use more cores?

Core Settings In Windows 10 Type ‘msconfig’ into the Windows Search Box and hit Enter. Select the Boot tab and then Advanced options. Check the box next to Number of processors and select the number of cores you want to use (probably 1, if you are having compatibility issues) from the menu. Select OK and then Apply.

Should I set max CPU State 99?

Minimum state should be as low as it’ll go, maximum should be 100%. Telling it to idle at 99% will only make it run hotter, not colder. It’s ok for an i7 7700k, this chip runs hotter. Intel said for the optimal life span to keep it below 75 C.

How do I isolate CPU cores in Linux?

5 Answers Add the parameter isolcpus=[cpu_number] to the Linux kernel command line from the boot loader during boot. Use IRQ affinity to set other CPUs to handle all interrupts so that your isolated CPU will not receive any interrupts. Use CPU affinity to fix your specific task to the isolated CPU.

How do I disable CPU cores in Ubuntu?

It is known the way to disable logical CPUs in Linux, basically with echo 0 > /sys/devices/system/cpu/cpu/online . This way, you are only telling to the OS to ignore that given ( ) CPU.

How does Linux handle CPU usage?

How To Check CPU Usage from Linux Command Line. top Command to View Linux CPU Load. mpstat Command to Display CPU Activity. sar Command to Show CPU Utilization. iostat Command for Average Usage. Other Options to Monitor CPU Performance. Nmon Monitoring Tool. Graphical Utility Option.

How many CPU cores do I have Ubuntu?

You can use one of the following command to find the number of physical CPU cores including all cores on Linux: lscpu command. cat /proc/cpuinfo. top or htop command. nproc command. hwinfo command. dmidecode -t processor command. getconf _NPROCESSORS_ONLN command.

Are cores the same as CPUs?

The main difference between CPU and Core is that the CPU is an electronic circuit inside the computer that carries out instruction to perform arithmetic, logical, control and input/output operations while the core is an execution unit inside the CPU that receives and executes instructions.

Does Linux use multiple cores?

Linux distributions have been multi-core and multi-thread in the kernel via SMP for years now. It is not the distribution that is important in this case, but the kernel. And since all major distributions are today based on the same kernel, just take your pick.

Is Zorin OS fast?

It’s Fast When speed is of the essence, Zorin OS really shines. Not only is its latest version faster than Ubuntu, its makers say, but it clocks in at a full four times faster than Windows 7.

Is Zorin fast?

Zorin OS runs lightning quick and doesn’t slow down with updates. Apps open fast, so you can spend more time being productive.

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Compile a C program with GCC, so that it can use all cpu cores in linux

I have a sample C program for addition. When I compile and run it with GCC it is using only one CPU core. Is there any way to compile a C program so that it can use all CPU cores in Linux. I used to compile like gcc -O3 malloc.c Code:

#include #include #include int main() < float *ptr; unsigned long long i; ptr = (float*) malloc(8000000000 * sizeof(float)); for(i=0; iclock_t tic = clock(); for(i=0; i clock_t toc = clock(); printf("Elapsed: %f seconds\n", (double)(toc - tic) / CLOCKS_PER_SEC); return 0; > 

If you use the make buildtool then you can use -j flag, where you can job simultaneously. For 4 cores you can give like make -j4 , is that what your asking?

@BasileStarynkevitch, I wasn’t sure what OP asked for, that’s why I just raised the question for clarification. If he wants to do this at runtime then I agree with you no point in using make .

4 Answers 4

Is there any way to compile a C program so that it can use all CPU cores in Linux.

No, not as magically as you want it to happen. Parallelization of programs is a very difficult subject and in general cannot be done automagically. BTW, parallel programs might not be as efficient as you wish them to be (be aware of Amdahl’s law).

However, you could design and code a parallel program. You might for example use posix threads. Beware, it is tricky! Read first some Pthread tutorial. You won’t be sure that all cores would be used (since they are managed by the kernel), but that is in practice very likely. Read also about processor affinity.

You could also use OpenMP or OpenACC. You could code some of your numerical kernels using OpenCL. You could have a multi-processing approach (e.g. forking several processes, using inter-process communications), perhaps using MPI. Look also into the MapReduce approach, the 0mq library (and many others).

You could read something on OSes, e.g. Operating Systems: Three Easy Pieces. You could also read something on Linux system programming, e.g. Advanced Linux Programming (or some newer book). See also intro(2) and syscalls(2) & pthreads(7).

Be aware that designing, coding and debugging a parallel (or concurrent, or distributed) application is very difficult. Take into account the cost of development time (and the time, probably years, needed to acquire the relevant skills). There is No Silver Bullet!

(it is not very realistic to transform an existing real-life sequential application into a parallel one; you usually have to design a parallel program from scratch)

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Making sort use all CPU CORES

htop is showing that the «sort» command only uses 1 CPU CORE (on an RPM based Linux distro). How can I tell it to use all the available CPU CORES?

2 Answers 2

—parallel=N change the number of sorts run concurrently to N

This was introduced in coreutils 8.6, with a lot of bugfixes in version 8.8. Older distros (e.g. RHEL6) don’t have this.

If you know the PID of the process, you could set the number of CPU cores as discussed here.

If you do not have taskset , you could install it as,

sudo yum install util-linux 

You could also launch the program mentioning specific CPU cores. So all these details are present in the above referenced link.

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