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how to set CPU affinity of a particular pthread?
Is there a way in Linux to disable one core for all processes except one process? I would like to have one core reserved only and only for my process.
Expected behavior is as follows:
Short answer, yes. A single core cpu(a processor), can run 2 or more threads simultaneously. These threads may belong to the one program, or they may belong different programs and thus processes. This type of multithreading is called Simultaneous MultiThreading(SMT).
As a general rule, 1 process only uses 1 core. Actually, 1 thread can only be executed by 1 core. If you have a dual core processor, it is literally 2 CPUs stuck together in the same pc. These are called physical processors.
If you want to prevent this and dedicate a whole CPU core to a particular program, you can use "isolcpus" kernel parameter, which allows you to reserve the CPU core during boot. Add the kernel parameter "isolcpus=" to the boot loader during boot or GRUB configuration file.
A multitasking operating system may just switch between processes to give the appearance of many processes executing simultaneously (that is, in parallel), though in fact only one process can be executing at any one time on a single CPU (unless the CPU has multiple cores, then multithreading or other similar ...
Yes, there is. You want to create two cpusets, one with your isolated CPU and the other with all the rest of the CPUs. Assign your special process to the isolated cpuset and all the rest of the processes to the other cpuset.
Here is a simple example script that will do it:
mkdir /cpuset mount -t cpuset none /cpuset/ cd /cpuset mkdir sys # create sub-cpuset for system processes /bin/echo 0-2 > sys/cpuset.cpus # assign cpus (cores) 0-2 to this set # adjust if you have more/less cores /bin/echo 1 > sys/cpuset.cpu_exclusive /bin/echo 0 > sys/cpuset.mems mkdir rt # create sub-cpuset for my process /bin/echo 3 > rt/cpuset.cpus # assign cpu (core) 3 to this cpuset # adjust this to number of cores-1 /bin/echo 1 > rt/cpuset.cpu_exclusive /bin/echo 0 > rt/cpuset.mems /bin/echo 0 > rt/cpuset.sched_load_balance /bin/echo 1 > rt/cpuset.mem_hardwall # move all processes from the default cpuset to the sys-cpuset for T in `cat tasks`; do echo "Moving " $T; /bin/echo $T > sys/tasks; done
Now start your process and find out its PID and go:
/bin/echo $PID > /cpuset/rt/tasks
If you want to revert these changes, just restart your system or do:
# move tasks back from sys-cpuset to root cpuset for T in `cat /cpuset/sys/tasks`; do echo "Moving " $T; /bin/echo $T > /cpuset/tasks; done # remove sys-cpuset rmdir /cpuset/sys # move tasks back from rt-cpuset to root cpuset for T in `cat /cpuset/rt/tasks`; do echo "Moving " $T; /bin/echo $T > /cpuset/tasks; done # remove rt-cpuset rmdir /cpuset/rt # unmount and remove /cpuset umount /cpuset rmdir /cpuset
Here is the man page: http://www.kernel.org/doc/man-pages/online/pages/man7/cpuset.7.html
There are also more complicated shell wrappers that can help you automate this, such as cset. See: http://web.archive.org/web/20120428093126/http://www.suse.com/documentation/slerte_11/slerte_tutorial/data/slerte_tutorial.html
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