Questions tagged [cpu]

The CPU (Central Processing Unit), is the chip in the computer that actually performs the operations and calculations that are done as a program runs. It is essentially what executes a program.

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32-bit, 64-bit CPU op-mode on Linux

I'm confused. Running Fedora Linux, lscpu yields: Architecture: i686 CPU op-mode(s): 32-bit, 64-bit ... But when I try to install a 64-bit program (Chrome) I get error like: ...
Zak's user avatar
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271 votes
6 answers
198k views

What do the flags in /proc/cpuinfo mean?

How can I tell whether my processor has a particular feature? (64-bit instruction set, hardware-assisted virtualization, cryptographic accelerators, etc.) I know that the file /proc/cpuinfo contains ...
Gilles 'SO- stop being evil''s user avatar
50 votes
4 answers
33k views

How can I set the processor affinity of a process on Linux?

How can I set the processor affinity of a process on Linux?
chillitom's user avatar
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34 votes
4 answers
141k views

Number of processors in /proc/cpuinfo

While I was learning about cpu load, I came to know that it depends on the number of cores. If I have 2 cores then load 2 will give 100% cpu utilization. So I tried to find out cores.( I already know ...
Madhurendra Sachan's user avatar
4 votes
2 answers
2k views

Is there a log of past threads that are now closed?

Sometimes, I have a rogue Java process which takes up 100% of my CPU and makes it jump about 30C in temperature (usually resulting in a crash if not killed). Problem is, I can never really identify ...
nopcorn's user avatar
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97 votes
2 answers
122k views

How to limit a process to one CPU core in Linux? [duplicate]

How to limit process to one cpu core ? Something similar to ulimit or cpulimit would be nice. (Just to ensure: I do NOT want to limit percentage usage or time of execution. I want to force app (with ...
Grzegorz Wierzowiecki's user avatar
261 votes
3 answers
419k views

Linux "top" command: What are us, sy, ni, id, wa, hi, si and st (for CPU usage)?

When I issue top in Linux, I get a result similar to this: One of the lines has CPU usage information represented like this: Cpu(s): 87.3%us, 1.2%sy, 0.0%ni, 27.6%id, 0.0%wa, 0.0%hi, 0.0%si, 0....
its_me's user avatar
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79 votes
15 answers
216k views

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 ...
doubledecker's user avatar
  • 1,807
67 votes
2 answers
90k views

Top and ps not showing the same cpu result

This is linked to this question. When I run top I get the following result: pid 3038 is using 18% cpu, however when running the result is 5.5%. And this number does not appear to be changing with ...
Theodor's user avatar
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353 votes
12 answers
693k views

How to know number of cores of a system in Linux?

I wanted to find out how many cores my system has, so I searched the same question in Google. I got some commands such as the lscpu command. When I tried this command, it gave me the following result: ...
Mr ASquare's user avatar
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82 votes
6 answers
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How to determine the maximum number to pass to make -j option?

I want to compile as fast as possible. Go figure. And would like to automate the choice of the number following the -j option. How can I programmatically choose that value, e.g. in a shell script? ...
tarabyte's user avatar
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33 votes
8 answers
25k views

cron Vs. sleep - which is the better one in terms of efficient cpu/memory utilization?

The Case: I need to run some commands/script at certain intervals of time and for this I have two options: set up a cron-job implement a loop with sleep in the script itself. Question: Which is the ...
rusty's user avatar
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80 votes
5 answers
177k views

So what are logical cpu cores (as opposed to physical cpu cores)?

I was googling about how I could find the number of CPUs in a machine and I found some posts but I am confused as some mentioned that you get the logical cores vs physical cores etc. So what is the ...
Jim's user avatar
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35 votes
2 answers
38k views

Understanding output of lscpu

You can see the output from lscpu command - jack@042:~$ lscpu Architecture: x86_64 CPU op-mode(s): 32-bit, 64-bit Byte Order: Little Endian CPU(s): 56 On-...
cph_sto's user avatar
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13 votes
4 answers
21k views

Setting running process affinity with taskset fails

I'm attempting to limit a process to a given number of CPU cores. According to the taskset man page and this documentation, the following should work: [fedora@dfarrell-opendaylight-cbench-devel ~]$ ...
dfarrell07's user avatar
8 votes
1 answer
6k views

Understanding core IDs

Just to understand core IDs: I have 4 CPUs: $ cat /proc/cpu* | grep proc* processor: 0 processor: 1 processor: 2 processor: 3 and the result of nproc is also 4. But if I use cat /proc/cpu* | grep '...
John Goofy's user avatar
6 votes
2 answers
3k views

How does load average work with modern CPU's?

My understanding of load average lead me to be quite shocked with my current system. The CPU in my workstation is an i7 with hyperthreading enabled, and cat /proc/cpuinfo produces 4 'cpu's. That all ...
Matthew Scharley's user avatar
82 votes
6 answers
303k views

What is the correct way to view your CPU speed on Linux?

I found two commands to output information about my CPU: cat /proc/cpuinfo and lscpu. /proc/cpuinfo shows that my CPU speed is 2.1 Ghz, whereas lspcu says it is 3167 Mhz. Which one is correct? This ...
Rohan's user avatar
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57 votes
9 answers
61k views

how to find out the cpu "code name" (architecture family)?

I get access to some xeon machines for checking performance. I want to find out what architecture they are using such as Haswell, Sandybridge , Ivybridge. Is there a command to find this out?
a curious engineer's user avatar
50 votes
8 answers
91k views

Limiting processes to not exceed more than 10% of CPU usage

I operate a Linux system which has a lot of users but sometimes an abuse occurs; where a user might run a single process that uses up more than 80% of the CPU/Memory. So is there a way to prevent ...
Giovanni Mounir's user avatar
22 votes
2 answers
62k views

disabling cpu cores on quad core processor on linux

I want to disable 3 CPU cores and run my processor on a single core. I have used command:maxcpus=1. But after this I executed this command ls /sys/devices/system/cpu. It still shows cpu0,cpu1,cpu2,...
user3818847's user avatar
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22 votes
4 answers
35k views

Why is kworker consuming so many resources on Linux 3.0.0-12-server?

Last Friday I upgraded my Ubuntu server to 11.10, which now runs with a 3.0.0-12-server kernel. Since then the overall performance has dropped dramatically. Before the upgrade the system load was ...
mailq's user avatar
  • 403
15 votes
5 answers
10k views

Understanding top and load average

I'm observing a high load average on a certain machine (about 9) in all three load fields. I understand load as the number of processes in state "run" / currently desiring CPU time. Am I correct at ...
Gabriel Schreiber's user avatar
14 votes
4 answers
15k views

Determining the particular processor on which a process is running

I have access to an 8-core node of a Linux cluster. When logged in to the node, I can see a list of processors using this command: more /proc/cpuinfo In my 8-core node, the processors are numbered ...
Andrew's user avatar
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4 votes
1 answer
2k views

How does the kernel assign cpu ids to physical cores?

One may find a lot of info about how to inspect physical cores layout in a running linux system, but I'm wondering how the physical cores are assigned a cpu id in the first place. After experiencing ...
Davide's user avatar
  • 273
111 votes
2 answers
427k views

Understanding %CPU while running top command [duplicate]

I am trying to understand what %CPU means when I run top. I am seeing %CPU for my application at "400" or "500" most of the time. Does anyone know what this means? 19080 david 20 ...
david's user avatar
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34 votes
2 answers
20k views

What does the "bugs" section of /proc/cpuinfo actually show?

On a Debian Stretch and testing/Buster system with a current kernel and installed microcode I still see meltdown and spectre listed as bugs in /proc/cpuinfo. However, running the spectre-meltdown-...
hurrbert's user avatar
  • 341
29 votes
4 answers
6k views

Why are some Intel family 6 CPU models (Core 2, Pentium M) not supported by intel_idle?

I've been tuning my Linux kernel for Intel Core 2 Quad (Yorkfield) processors, and I noticed the following messages from dmesg: [ 0.019526] cpuidle: using governor menu [ 0.531691] clocksource: ...
Parker's user avatar
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26 votes
5 answers
59k views

How do I know which processors are physical cores?

I've got an Intel i7 2700k here, and I'd like to know how I can tell which processors are physical and which are virtual (ie: hyperthreading). I'm currently running a Conky script to display my CPU ...
Naftuli Kay's user avatar
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19 votes
1 answer
12k views

What are Kernel PMU event-s in perf_events list?

Searching for what one can monitor with perf_events on Linux, I cannot find what Kernel PMU event are? Namely, with perf version 3.13.11-ckt39 the perf list shows events like: branch-instructions OR ...
xealits's user avatar
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18 votes
1 answer
4k views

How does a CPU know there is IO pending?

I have been looking into the iowait property shown in top utility output as shown below. top - 07:30:58 up 3:37, 1 user, load average: 0.00, 0.01, 0.05 Tasks: 86 total, 1 running, 85 ...
Alchemist's user avatar
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15 votes
7 answers
48k views

Getting cpu usage same every time.

When I execute following command to get cpu usage , I get nice + user cpu usage. top -b -n1 | grep "Cpu(s)" | awk '{print $2 + $4}' Output: 14.5 Here I am getting problem is that the output ...
KK Patel's user avatar
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11 votes
2 answers
12k views

Why does top report the incorrect CPU usage?

I have a machine with Intel(R) Xeon(R) CPU E5520 visible as 16 logical cores (8 with HT). If I run something to eat CPU time (single threaded) top correctly reports 100% CPU usage for the process but ...
user avatar
11 votes
2 answers
123k views

Debian jessie boot hangs at "Started Update UTMP about System Runlevel Changes."

I just upgraded my MOBO and CPU on my PC, and now whenever I try and boot my debian install it hangs at [ OK ] Started Update UTMP about System Runlevel Changes. Is there an way I can boot into my ...
randomdev2's user avatar
11 votes
1 answer
18k views

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 ...
Chris Tsui's user avatar
11 votes
2 answers
12k views

what is the difference between cpu and core?

The output of lscpu of my pc looks like -- Architecture: x86_64 CPU op-mode(s): 32-bit, 64-bit Byte Order: Little Endian CPU(s): 4 On-line CPU(s) list: 0-3 ...
alhelal's user avatar
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9 votes
2 answers
13k views

How to disable one CPU

I'm trying to disable some CPUs of my server. I've found this link: https://www.cyberciti.biz/faq/debian-rhel-centos-redhat-suse-hotplug-cpu/linux-turn-on-off-cpu-core-commands/, which offers me a ...
Yves's user avatar
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7 votes
3 answers
2k views

Debian not showing all cores?

I recently purchased a i5-9600K. Which is supposed to run 6 cores and 6 threads (hyperthreading), when I take a look into /proc/cpuinfo the ht flag is on, and checking a tool like htoponly shows 6 ...
wiitohzjeh's user avatar
7 votes
3 answers
3k views

Externaly limiting number of CPU cores used

I need to externally limit a process/session to a certain number of cores. Are there any other possibilities than CPU affinity (I don't like the need to specify the actual cores) and cgroups (hard to ...
Šimon Tóth's user avatar
  • 8,238
3 votes
2 answers
2k views

Pipe Viewer - Progress monitor performance consequence

I am writing a batch script to sort through gigs and gigs of data. All of the data is text but the script will take a long long time to execute. I would like to give some visual indication that the ...
Dylan's user avatar
  • 1,038
3 votes
1 answer
2k views

How does the Linux kernel schedule CPU, between user space processes/threads and kernel tasks/jobs

I was trying to understand the Linux process management and scheduling. I know that the scheduler schedules different processes based on priority/time slicing. But there are kernel tasks (I am not ...
Franc's user avatar
  • 289
3 votes
2 answers
3k views

Why is cpu_idle called as the last function of the start_kernel routine?

I'm reading the start_kernel function in /init/main.c. The last function called in start_kernel is rest_init, and at the end of rest_init, cpu_idle is called. Why is it called as the last function ...
Anthony's user avatar
  • 31
2 votes
1 answer
297 views

How can I prevent installation of a specific package on Linux Mint?

TL;DR Question: How can I disallow installing of the package intel-microcode in the future? With my bad memory, I may try installing it someday, again. Long story Yesterday, I installed the intel-...
Vlastimil Burián's user avatar
0 votes
1 answer
10k views

How to get the number of processes waiting for CPU on Linux?

If CPU is running 100% usage, other processes should be put inside a run queue. Which command can I use to get the size of the run-queue? vmstat seems to return a related value of the CPU like below: ...
Joey Yi Zhao's user avatar
0 votes
2 answers
6k views

How to restrict awk math output to 2 decimal places

My Command is below and its print Free CPU and Used CPU below format. I want to restrict awk output to 2 decimal place. grep 'cpu ' /proc/stat | awk '{usage=($2+$4)*100/($2+$4+$5)} {free=($5)*100/($...
Sandeep Singh's user avatar
86 votes
3 answers
31k views

What does an idle CPU process do?

Looking at the source of strace I found the use of the clone flag CLONE_IDLETASK which is described there as: #define CLONE_IDLETASK 0x00001000 /* kernel-only flag */ After looking deeper into it I ...
grochmal's user avatar
  • 8,647
50 votes
5 answers
238k views

How to find which Process is causing High CPU usage

Is there any way to find out from terminal which process is causing high CPU Usage ? It would also be useful to order processes in descending order of cpu Usage
Gautam's user avatar
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47 votes
1 answer
94k views

What are software and hardware interrupts, and how are they processed?

I am not sure if I understand the concept of hardware and software interrupts. If I understand correctly, the purpose of a hardware interrupt is to get some attention of the CPU, part of implementing ...
Tim's user avatar
  • 102k
26 votes
1 answer
4k views

High CPU usage with CFS?

I asked a previous question to try and isolate the source of an increase in CPU usage when moving an application from RHEL 5 to RHEL 6. The analysis that I did for that seems to indicate that it is ...
Dave Johansen's user avatar
23 votes
4 answers
31k views

Run Linux process at very very low priority?

I have a regular process that's not so important but will consume very much CPU power. I have another process which is really important, but it spends most of the time idle, but when it gets a job it ...
uray's user avatar
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