{"id":7015,"date":"2018-10-12T14:19:48","date_gmt":"2018-10-12T11:19:48","guid":{"rendered":"https:\/\/www.howtoforge.com\/linux-taskset-command\/"},"modified":"2018-10-12T14:19:48","modified_gmt":"2018-10-12T11:19:48","slug":"linux-taskset-command-tutorial-for-beginners-with-examples","status":"publish","type":"post","link":"https:\/\/afaghhosting.net\/blog\/linux-taskset-command-tutorial-for-beginners-with-examples\/","title":{"rendered":"Linux taskset Command Tutorial for Beginners (with Examples)"},"content":{"rendered":"

Ever heard of the term processor affinity? It’s a feature that allows you to bind or unbind processes to a particular central processing unit, or a range of CPUs. Yes, you can tell the system which CPU core(s) should be used to a run a particular process. For theoretical details on why processor affinity exists, head here<\/a>.<\/p>\n

Here, in this tutorial, we will discuss a utility – dubbed taskset<\/strong> – that lets you achieve processor affinity. But before we do that, it’s worth mentioning that all examples in this tutorial have been tested on an Ubuntu 18.04 LTS machine.<\/p>\n

Linux taskset command<\/h2>\n

The taskset command allows you to set or retrieve a process’s CPU affinity. Following is its syntax:<\/p>\n

taskset [options] mask command [argument…]
taskset [options] -p [mask] pid<\/p>\n

Here’s how the tool’s man page explains it:<\/p>\n

 taskset\u00a0 is\u00a0 used\u00a0 to\u00a0 set\u00a0 or\u00a0 retrieve\u00a0 the CPU affinity of a running\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 process given its pid, or to launch a new\u00a0 command\u00a0 with\u00a0 a\u00a0 given\u00a0 CPU\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 affinity.\u00a0\u00a0 CPU affinity is a scheduler property that \"bonds\" a process\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 to a given set of CPUs on the system.\u00a0 The Linux scheduler\u00a0 will\u00a0 honor\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 the\u00a0 given CPU affinity and the process will not run on any other CPUs.\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 Note that the Linux scheduler also supports natural CPU\u00a0 affinity:\u00a0 the\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 scheduler attempts to keep processes on the same CPU as long as practi?\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 cal for performance reasons.\u00a0 Therefore, forcing a specific CPU\u00a0 affin?\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 ity is useful only in certain applications.
\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 The CPU affinity is represented as a bitmask, with the lowest order bit\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 corresponding to the first logical CPU and the highest order bit corre?\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 sponding\u00a0 to\u00a0 the\u00a0 last logical CPU.\u00a0 Not all CPUs may exist on a given\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 system but a mask may specify more CPUs than are present.\u00a0 A\u00a0 retrieved\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 mask\u00a0 will\u00a0 reflect only the bits that correspond to CPUs physically on\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 the system.\u00a0 If an invalid mask is given (i.e., one that corresponds to\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 no\u00a0 valid\u00a0 CPUs on the current system) an error is returned.\u00a0 The masks\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 may be specified in hexadecimal (with or without a leading \"0x\"), or as\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 a CPU list with the --cpu-list option.\u00a0 For example,<\/p>
\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 0x00000001\u00a0 is processor #0,<\/p>
\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 0x00000003\u00a0 is processors #0 and #1,<\/p>
\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 0xFFFFFFFF\u00a0 is processors #0 through #31,<\/p>
\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 32\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 is processors #1, #4, and #5,<\/p>
\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 --cpu-list 0-2,6\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 is processors #0, #1, #2, and #6.<\/p>
\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 When\u00a0 taskset returns, it is guaranteed that the given program has been\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 scheduled to a legal CPU.<\/p><\/pre>\n
Following are some Q&A-styled examples that should give you a better idea on how the taskset command works.<\/p>\n
Q1. How to use taskset to\u00a0retrieve CPU affinity of a process?<\/h2>\n
If you want taskset to display CPU affinity of an already running process, use the command in the following way:<\/p>\n
taskset -p [PID]<\/p>\n
Just replace PID with the ID of the process whose CPU affinity you want to fetch. For example:<\/p>\n
taskset -p 9726<\/p>\n
The above command returned the following output:<\/p>\n
pid 9726's current affinity mask: f<\/pre>\n
So hexadecimal value ‘f’ here means the process can run on any of the 4 processor cores: 0,1,2,3.<\/p>\n
If you want the output to be in terms of CPU range, you can add the -c command line option.<\/p>\n
taskset -cp 9726<\/p>\n
Following is the output in this case:<\/p>\n
pid 9726's current affinity list: 0-3<\/pre>\n
Q2. How to change CPU affinity using taskset?<\/h2>\n
To tweak the CPU affinity of an existing process, you need to specify the process ID (like we did in the previous section) along with a hexadecimal mask that defines the new affinity.<\/p>\n
For example, the current CPU affinity of the Gedit process (PID: 9726) is ‘f’.<\/p>\n
\"How<\/a><\/p>\n
To change the affinity to 0x11, use the following command:<\/p>\n
taskset -p 0x11 9726<\/p>\n
And then you can again check the new affinity using the following command:<\/p>\n
taskset -p 9726<\/p>\n
The following screenshots show the outputs for these commands in my case:<\/p>\n
\"Using<\/a><\/p>\n
So you can see that the affinity got changed.<\/p>\n
Q3. How to assign a range of CPUs while changing affinity?<\/h2>\n
This is no big deal. All you have to do is to add the -c command line option to the command we’ve used in the previous section along with the CPU core range as input.<\/p>\n
Here is an example:<\/p>\n
taskset -cp 0,3 9726<\/p>\n
Following is the output produced in this case:<\/p>\n
pid 9726's current affinity list: 0pid 9726's new affinity list: 0,3<\/pre>\n
Q4. How to launch a process with predefined CPU affinity?<\/h2>\n
Yes, you can also launch a process with a set CPU affinity.<\/p>\n
For example, I launched the text gedit editor with CPU affinity 0xa.<\/p>\n
taskset 0xa gedit<\/p>\n
Conclusion<\/h2>\n
Agreed, the taskset command isn’t for an average command line user. It’s mostly used by server side experts for process optimization in a multi core environment. We’ve discussed the tool’s bascs here. For more info, head to its man page<\/a>.<\/p>\n
\n\"Himanshu <\/p>\n
About Himanshu Arora<\/strong><\/p>\n
Himanshu Arora has been working on Linux since 2007. He carries professional experience in system level programming, networking protocols, and command line. In addition to HowtoForge, Himanshu’s work has also been featured in some of world’s other leading publications including Computerworld, IBM DeveloperWorks, and Linux Journal.<\/p>\n<\/div>\n
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Ever heard of the term processor affinity? It’s a feature that allows you to bind or unbind processes to a particular central processing unit, or a range of CPUs. Yes, you can tell the system which CPU core(s) should be used to a run a particular process. For theoretical details on why processor affinity exists, […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[36],"tags":[],"class_list":["post-7015","post","type-post","status-publish","format-standard","hentry","category-36"],"_links":{"self":[{"href":"https:\/\/afaghhosting.net\/blog\/wp-json\/wp\/v2\/posts\/7015","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/afaghhosting.net\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/afaghhosting.net\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/afaghhosting.net\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/afaghhosting.net\/blog\/wp-json\/wp\/v2\/comments?post=7015"}],"version-history":[{"count":0,"href":"https:\/\/afaghhosting.net\/blog\/wp-json\/wp\/v2\/posts\/7015\/revisions"}],"wp:attachment":[{"href":"https:\/\/afaghhosting.net\/blog\/wp-json\/wp\/v2\/media?parent=7015"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/afaghhosting.net\/blog\/wp-json\/wp\/v2\/categories?post=7015"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/afaghhosting.net\/blog\/wp-json\/wp\/v2\/tags?post=7015"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}