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Bug#914758: linux-image-4.18.0-2-amd64: setting elevator=none does not change io scheduler

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  Bug#914758: linux-image-4.18.0-2-amd64: setting elevator=none does not change io scheduler Matt Zagrabelny <mzagrabe@d.umn.edu> - 2018-11-27 01:20 +0100
    Bug#914758: linux-image-4.18.0-2-amd64: setting elevator=none does not change io scheduler Ben Hutchings <ben@decadent.org.uk> - 2018-11-27 04:00 +0100
    Processed: Re: Bug#914758: linux-image-4.18.0-2-amd64: setting  elevator=none does not change io scheduler "Debian Bug Tracking System" <owner@bugs.debian.org> - 2018-11-27 04:00 +0100

#62560 — Bug#914758: linux-image-4.18.0-2-amd64: setting elevator=none does not change io scheduler

Package: src:linux
Version: 4.18.10-2
Severity: normal

Greetings!

Thank you for your contribution to Debian. It is appreciated!

I am running:

linux-image-4.18.0-2-amd64 4.18.10-2+b1

and attempting to set the IO scheduler.

Looking at the current scheduler:

# cat /sys/block/sda/queue/scheduler
[mq-deadline] none

However my kernel command line:

# cat /proc/cmdline
BOOT_IMAGE=/boot/vmlinuz-4.18.0-2-amd64 root=UUID=1965daa6-aa4c-4c02-8402-589867e32517 ro elevator=none quiet

I can set the scheduler via sysfs:

# echo none > /sys/block/sda/queue/scheduler
# cat /sys/block/sda/queue/scheduler
[none] mq-deadline

I just don't know why the elevator parameter isn't working. According to the
kernel documentation for 4.18:

grep -A3 elevator /usr/src/linux-source-4.18/Documentation/admin-guide/kernel-parameters.txt
elevator=       [IOSCHED]
                Format: {"cfq" | "deadline" | "noop"}
                See Documentation/block/cfq-iosched.txt and
                Documentation/block/deadline-iosched.txt for details.

It appears that I should pass "noop" to the elevator parameter. However, the
same results occur:

# cat /proc/cmdline
BOOT_IMAGE=/boot/vmlinuz-4.18.0-2-amd64 root=UUID=1965daa6-aa4c-4c02-8402-589867e32517 ro elevator=noop quiet

# cat /sys/block/sda/queue/scheduler
[mq-deadline] none

If I look at the kernel ring buffer I see some evidence that I perhaps should
be using the "noop" scheduler:

[    0.000000] Command line: BOOT_IMAGE=/boot/vmlinuz-4.18.0-2-amd64 root=UUID=1965daa6-aa4c-4c02-8402-589867e32517 ro elevator=noop quiet
[    0.000000] Kernel command line: BOOT_IMAGE=/boot/vmlinuz-4.18.0-2-amd64 root=UUID=1965daa6-aa4c-4c02-8402-589867e32517 ro elevator=noop quiet
[    0.432773] Block layer SCSI generic (bsg) driver version 0.4 loaded (major 248)
[    0.432794] io scheduler noop registered (default)
[    0.432795] io scheduler deadline registered
[    0.432825] io scheduler cfq registered
[    0.432826] io scheduler mq-deadline registered

I see the same io scheduler registerd when I use "elevator=none", too. That is
"none" is not registered, but "noop" is.

I don't see anything in my udev configs that would be setting the scheduler.
This is a VM system.

Thanks for any help!



-- Package-specific info:
** Kernel log: boot messages should be attached


-- System Information:
Debian Release: buster/sid
  APT prefers unstable
  APT policy: (500, 'unstable'), (500, 'testing'), (500, 'stable'), (500, 'oldstable'), (1, 'experimental')
Architecture: amd64 (x86_64)

Kernel: Linux 4.17.0-3-amd64 (SMP w/8 CPU cores)
Locale: LANG=en_US.UTF-8, LC_CTYPE=en_US.UTF-8 (charmap=UTF-8), LANGUAGE=en_US.UTF-8 (charmap=UTF-8)
Shell: /bin/sh linked to /bin/dash
Init: systemd (via /run/systemd/system)
LSM: AppArmor: enabled

Versions of packages linux-image-4.18.0-2-amd64 depends on:
ii  initramfs-tools [linux-initramfs-tool]  0.132
ii  kmod                                    25-1
ii  linux-base                              4.5

Versions of packages linux-image-4.18.0-2-amd64 recommends:
ii  apparmor             2.13.1-3+b1
ii  firmware-linux-free  3.4
ii  irqbalance           1.5.0-0.1

Versions of packages linux-image-4.18.0-2-amd64 suggests:
pn  debian-kernel-handbook  <none>
ii  extlinux                3:6.04~git20171011.af7e95c3+dfsg1-5
ii  grub-pc                 2.02+dfsg1-8
pn  linux-doc-4.18          <none>

Versions of packages linux-image-4.18.0-2-amd64 is related to:
ii  firmware-amd-graphics     20180825+dfsg-1
pn  firmware-atheros          <none>
pn  firmware-bnx2             <none>
pn  firmware-bnx2x            <none>
pn  firmware-brcm80211        <none>
pn  firmware-cavium           <none>
pn  firmware-intel-sound      <none>
pn  firmware-intelwimax       <none>
pn  firmware-ipw2x00          <none>
pn  firmware-ivtv             <none>
pn  firmware-iwlwifi          <none>
pn  firmware-libertas         <none>
ii  firmware-linux-nonfree    20180825+dfsg-1
ii  firmware-misc-nonfree     20180825+dfsg-1
pn  firmware-myricom          <none>
pn  firmware-netxen           <none>
pn  firmware-qlogic           <none>
pn  firmware-realtek          <none>
pn  firmware-samsung          <none>
pn  firmware-siano            <none>
pn  firmware-ti-connectivity  <none>
pn  xen-hypervisor            <none>

-- no debconf information

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#62563

[Multipart message — attachments visible in raw view] — view raw

Control: tag -1 upstream
Control: retitle -1 Missing equivalent of elevator kernel parameter for blk-mq

On Mon, 2018-11-26 at 18:10 -0600, Matt Zagrabelny wrote:
> Package: src:linux
> Version: 4.18.10-2
> Severity: normal
> 
> Greetings!
> 
> Thank you for your contribution to Debian. It is appreciated!
> 
> I am running:
> 
> linux-image-4.18.0-2-amd64 4.18.10-2+b1
> 
> and attempting to set the IO scheduler.
> 
> Looking at the current scheduler:
> 
> # cat /sys/block/sda/queue/scheduler
> [mq-deadline] none

This is a device implemented using the "blk-mq" API, which was
introduced a few years ago but has only recently come to be used by
most block devices.

[...]
> I just don't know why the elevator parameter isn't working. According to the
> kernel documentation for 4.18:
> 
> grep -A3 elevator /usr/src/linux-source-4.18/Documentation/admin-guide/kernel-parameters.txt
> elevator=       [IOSCHED]
>                 Format: {"cfq" | "deadline" | "noop"}
>                 See Documentation/block/cfq-iosched.txt and
>                 Documentation/block/deadline-iosched.txt for details.
[...]

This is correct, but incomplete.  The "elevator" kernel parameter only
controls the default schedulers for the old "blk-rq" device API.

Unfortunately, because of the differences between the old and new APIs
it was also necessary to introduce a new set of schedulers.  There
isn't (yet) a kernel parameter to choose the default for blk-mq
devices.

Ben.

-- 
Ben Hutchings
Beware of bugs in the above code;
I have only proved it correct, not tried it. - Donald Knuth

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#62564 — Processed: Re: Bug#914758: linux-image-4.18.0-2-amd64: setting elevator=none does not change io scheduler

Processing control commands:

> tag -1 upstream
Bug #914758 [src:linux] linux-image-4.18.0-2-amd64: setting elevator=none does not change io scheduler
Added tag(s) upstream.
> retitle -1 Missing equivalent of elevator kernel parameter for blk-mq
Bug #914758 [src:linux] linux-image-4.18.0-2-amd64: setting elevator=none does not change io scheduler
Changed Bug title to 'Missing equivalent of elevator kernel parameter for blk-mq' from 'linux-image-4.18.0-2-amd64: setting elevator=none does not change io scheduler'.

-- 
914758: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=914758
Debian Bug Tracking System
Contact owner@bugs.debian.org with problems

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