How do I change to the noop scheduler?

Question

I have an SSD in my laptop and I've been told that switching to the "noop" scheduler is preferred.

How do I change to the noop scheduler, and where do I make the change so that it is persistent across reboots?

Eliah Kagan · Answer 1 · 2011-11-13T03:54:47.280

31

Suppose your hard disk is /dev/sda. Then you could check to see what scheduler is currently in use for it:

cat /sys/block/sda/queue/scheduler

(The scheduler currently in use will be surrounded by [ ] brackets.)

And you could make it use the noop scheduler:

echo noop > /sys/block/sda/queue/scheduler

See this article for slightly more information.

To make the change persist, you can put the command in /etc/rc.local.

edited Nov 13 '11 at 03:54

answered Nov 13 '11 at 03:33

Eliah Kagan

117,780

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I get a "permission denied" error running this, even with sudo – Lucas Bustamante Jun 17 '19 at 17:46
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@LucasBustamante Are you running sudo echo noop > /sys/block/sda/queue/scheduler? That doesn't work, as the shell, which runs as your user, sets up the redirection before running the command whose output is redirected. You can use echo noop | sudo tee /sys/block/sda/queue/scheduler instead. See Cannot echo “hello” > x.txt even with sudo? and How to solve “permission denied” when using sudo with redirection in Bash? for more information and other approaches. (If that's not what you mean, please let me know.) – Eliah Kagan Jun 17 '19 at 17:53
thanks for answering, that didn't help either. I'm using a NVMe SSD, I think it doesn't use the scheduler at all, from what I understood https://serverfault.com/questions/693348/what-does-it-mean-when-linux-has-no-i-o-scheduler – Lucas Bustamante Jun 17 '19 at 19:09

score 24 · Accepted Answer · answered Nov 24 '11 at 23:12

24

Edit /etc/default/grub, such as gksudo gedit /etc/default/grub, here you need to add elevator=noop.

Change GRUB_CMDLINE_LINUX_DEFAULT="quiet splash" to GRUB_CMDLINE_LINUX_DEFAULT="quiet splash elevator=noop".

Then run sudo update-grub2 and restart.

answered Nov 24 '11 at 23:12

Anonymous

11,699

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Anonymous' answer is good for changing the default across all disks on a system. By contrast, Eliah Kagan's answer sets the default for specific disks. For a laptop with a single drive, either works fine. For systems with multiple disks -- most notably, disks with both SSDs and rotating drives), Eliah Kagan's answer provides finer-grained control. – Royce Williams May 29 '14 at 07:15
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The elevator= kernel argument was removed in kernel v5.4, which is used since Ubuntu 20.04 LTS focal. https://github.com/torvalds/linux/commit/85c0a037dc7a1a34d6add49d6eaa2deddbf43d7b – Paul Tobias Apr 24 '20 at 08:58

score 14 · Answer 3 · answered May 29 '14 at 15:48

14

This Debian reference shows how to dynamically detect SSDs and change the scheduler accordingly:

In systems with different drive types you can adjust settings with a udev rule (create /etc/udev/rules.d/60-ssd-scheduler.rules):

# Set deadline scheduler for non-rotating disks
 ACTION=="add|change", KERNEL=="sd[a-z]", ATTR{queue/rotational}=="0",ATTR{queue/scheduler}="deadline"

To make sure that your kernel can detect rotational status:

$ for f in /sys/block/sd?/queue/rotational; do printf "$f is "; cat $f; done
/sys/block/sda/queue/rotational is 1
/sys/block/sdb/queue/rotational is 1
/sys/block/sdc/queue/rotational is 0   <=== Only this is SSD!

All of the above is quoted directly from the Debian reference, which has many other elements of interest to first-time SSD users.

answered May 29 '14 at 15:48

Royce Williams

286

root@titan:/home/kessaras# for f in /sys/block/sd?/queue/rotational; do printf "$f is "; cat $f; done /sys/block/sda/queue/rotational is 0 /sys/block/sdb/queue/rotational is 0 /sys/block/sdc/queue/rotational is 1 /sys/block/sdd/queue/rotational is 1
root@titan:/home/kessaras# cat /sys/block/sd*/queue/scheduler [mq-deadline] none [mq-deadline] none [mq-deadline] none [mq-deadline] none

Something is very wrong here. It changes all the hard disks to deadline
– Pavlos Theodorou Aug 14 '19 at 16:57
The command doesn't change anything - it simply reports whether a disk is "rotational" (HDD). Rotational = 0 means it's an SSD or other non-spinning drive. – Royce Williams Aug 14 '19 at 17:05
what do you mean it doesnt change anything ? And the udev rule written there what does it do ? It is inside a yellow box too. You mean that im blind or i can't read ? – Pavlos Theodorou Aug 15 '19 at 13:07
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My mistake. It seems in latest kernel they removed the schedulers... ??? for f in /sys/block/sd?/queue/scheduler; do printf "$f is "; cat $f; done /sys/block/sda/queue/scheduler is [mq-deadline] none /sys/block/sdb/queue/scheduler is [mq-deadline] none /sys/block/sdc/queue/scheduler is [mq-deadline] none /sys/block/sdd/queue/scheduler is [mq-deadline] none
The article and everything you wrote is fine. It's just that there is only deadline and nothing else to choose from.
– Pavlos Theodorou Aug 15 '19 at 13:24

score 1 · Answer 4 · edited Feb 24 '20 at 16:41

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vi /etc/rc.local

Add line

for f in /sys/block/sd?/queue/scheduler; do echo "noop" > $f; cat $f; done

Then run the command

chmod +x /etc/rc.local

edited Feb 24 '20 at 16:41

Tejas Lotlikar

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answered Feb 24 '20 at 14:21

mdobrzyn

11

How do I change to the noop scheduler?

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