Linux's Multi-Queue Block Code Still Presenting Some Performance Regressions

[phoronix]

Phoronix: Linux's Multi-Queue Block Code Still Presenting Some Performance Regressions

For those thinking of switching to the new multi-queue block layer, a.k.a. blk-mq, be forewarned that there are still some regressions outstanding...

http://www.phoronix.com/scan.php?page=news_item&px=Linux-MQ-Perf-Regressions

[latalante]

This new series of patches clearly improves performance.
git clone -b blk-mq-dispatch_for_scsi.V4 https://github.com/ming1/linux

You can always come back CFQ or deadline, with kernel boot parameters:
scsi_mod.use_blk_mq=0 elevator=cfq

[czz0]

Kyber is by far the best scheduler I've tried in terms of fairness and desktop latency under high read/write tasks. Much better than BFQ or CFQ. With any other scheduler if I copy a large file to the drive my OS is on, and then try to open a program it might not even open until the file is done being copied, any desktop task that requires reading/writing from the drive is stalled or extremely slow. Kyber is the only scheduler I've used that prevents that from happening, I've tried every other available disk scheduler.

[halo9en]

Quoting myself...

I'd really like to see BFQ vs Kyber vs CFQ benchmarks for latency / responsiveness. Kyber seems smaller and has good throughput, but I wonder which one is better for responsiveness (regular desktop usage and media)

[Vistaus]

Kyber is by far the best scheduler I've tried in terms of fairness and desktop latency under high read/write tasks. Much better than BFQ or CFQ. With any other scheduler if I copy a large file to the drive my OS is on, and then try to open a program it might not even open until the file is done being copied, any desktop task that requires reading/writing from the drive is stalled or extremely slow. Kyber is the only scheduler I've used that prevents that from happening, I've tried every other available disk scheduler.

How do I set Kyber as my scheduler? (I can only find how to set BFQ as my scheduler)

[geearf]

How do I set Kyber as my scheduler? (I can only find how to set BFQ as my scheduler)

It's the same thing since they're both blk_mq schedulers.

[Vistaus]

It's the same thing since they're both blk_mq schedulers.

So you're saying that if I set the Linux CMD line to use blk_mq at boot I'm automatically using Kyber?

[geearf]

So you're saying that if I set the Linux CMD line to use blk_mq at boot I'm automatically using Kyber?

No, I am saying you can follow a tutorial for BFQ and instead type Kyber when you're setting the scheduler.

Same Linux command for both (it's only about blk_mq).
Almost same udev rule, just one has the word BFQ and the other has Kyber.

[Vistaus]

No, I am saying you can follow a tutorial for BFQ and instead type Kyber when you're setting the scheduler.

Same Linux command for both (it's only about blk_mq).
Almost same udev rule, just one has the word BFQ and the other has Kyber.

Ah, okay, thanks. Which tutorial did you follow? 'Cause I found a few for BFQ but no matter BFQ or Kyber, the scheduler remains 'mq-deadline' :/

[geearf]

Ah, okay, thanks. Which tutorial did you follow? 'Cause I found a few for BFQ but no matter BFQ or Kyber, the scheduler remains 'mq-deadline' :/

I don't remember, but here's what I've done:

Linux command line addon: scsi_mod.use_blk_mq=1
(you can use dm_mod as well for the device mapper I believe, I don't use it)
udev rule: ACTION=="add|change", KERNEL=="sd[a-z]", ATTR{queue/scheduler}="bfq"
retrigger udev: udevadm control --reload && udevadm trigger
or simply restart the system.

Adjust as needed for kyber/your system.

The simplest way to change your scheduler is of course: echo kyber >| /sys/block/sdX/queue/scheduler (replace X appropriately).
That will only work once you are on blk_mq, but that seems to be your case already so that's fine.

Although, one thing to check, just in case, make sure you have kyber available, if it's not in: cat /sys/block/sd*/queue/scheduler, you may have to rebuild your kernel.