Arch Linux

travishume

Member

Registered: 2012-11-03

Posts: 10

huh. Where'd the IO schedulers go?

I've been running linux-ck-haswell for a long time. Just noticed that sda was using CFQ instead of BFQ. I tried to change it and discovered that the only schedulers available are noop, deadline and cfq.
During boot the kernel says it's registering noop, deadline, cfq, mq-deadline, kyber, and bfq.

╭─╴ ~ 
╰╴► s journalctl --this-boot |grep scheduler
Mar 23 15:04:37 wumpy kernel: io scheduler noop registered
Mar 23 15:04:37 wumpy kernel: io scheduler deadline registered
Mar 23 15:04:37 wumpy kernel: io scheduler cfq registered (default)
Mar 23 15:04:37 wumpy kernel: io scheduler mq-deadline registered
Mar 23 15:04:37 wumpy kernel: io scheduler kyber registered
Mar 23 15:04:37 wumpy kernel: io scheduler bfq registered

╭─╴ ~ 
╰╴► cat /sys/block/sda/queue/scheduler      
noop deadline [cfq] 

╭─╴ ~ 
╰╴► echo bfq |sudo tee /sys/block/sda/queue/scheduler
bfq
tee: /sys/block/sda/queue/scheduler: Invalid argument

Been searching around for a possible regression but haven't found anyone else chattering about this.
I'm not a linux or arch newbie but have never seen this before. Ideas?

V1del

Forum Moderator

Registered: 2012-10-16

Posts: 21,728

Re: huh. Where'd the IO schedulers go?

Those are multi-queue schedulers, which you will have to activate via a kernel option currently. https://wiki.archlinux.org/index.php/Im … _scheduler

ooo

Member

Registered: 2013-04-10

Posts: 1,638

Re: huh. Where'd the IO schedulers go?

Ever since BFQ got approved in upsteam kernel (and not only available by patching the kernel), it is multi-queue scheduler, just like kyber and mq-deadline. I think you still need to enable multi-queue scheduling from kernel command line to use them, at least with SATA disks.

See https://wiki.archlinux.org/index.php/Im … _scheduler

EDIT. Oops, snaked by V1del

Last edited by ooo (2018-03-23 22:53:19)

travishume

Member

Registered: 2012-11-03

Posts: 10

Re: huh. Where'd the IO schedulers go?

Ok, a little more reading and I found the answer.

Note: The block multi-queue (blk-mq) mode must be enabled at boot time to be able to access the latest BFQ and Kyber schedulers. This is done by adding scsi_mod.use_blk_mq=1 to the kernel parameters. The single-queue schedulers are no longer available once in this mode.

Never used that kernel param before.

loqs

Member

Registered: 2014-03-06

Posts: 17,369

Re: huh. Where'd the IO schedulers go?

Please note https://bugs.archlinux.org/task/57496

blk-mq still has way too many issues and won't to be considered for patching.