This is a change in the kernel between 3.13 and 3.13-rc1. It also persists in the most recent kernel version. I believe this is still an invalid bug as what benefit would setting an I/O scheduler to anything be if the device is virtual? On a physical machine you are still able to set the I/O scheduler properly.
-- You received this bug notification because you are a member of Kernel Packages, which is subscribed to linux in Ubuntu. https://bugs.launchpad.net/bugs/1346687 Title: Ubuntu 14 KVM Guest I/O Elevator Non-configurable Status in “linux” package in Ubuntu: Invalid Bug description: Ubuntu 14.04 guest runs pretty much standard standard configuration: KVM hypervisor, ACPI and APIC enabled, virtio disk bus, raw storage format... While running this project, I am also involved in testing SSD drives across different Linux distributions and their support for discard option (TRIM). To cut the story short, Ubuntu-based KVM guest did not set any scheduler on the boot disk vda): # lsblk -io KNAME,TYPE,SCHED,ROTA,DISC-GRAN,DISC-MAX KNAME TYPE SCHED ROTA DISC-GRAN DISC-MAX sr0 rom deadline 1 0B 0B vda disk 1 0B 0B vda1 part 1 0B 0B vda2 part 1 0B 0B vda5 part 1 0B 0B dm-0 lvm 1 0B 0B dm-1 lvm 1 0B 0B That is in stark contrast with other distributions running almost identical KVM guest configuration (with the exception of the root file system using BTRFS instead of EXT4 on SUSE). Oracle Linux 6.5: # lsblk -io KNAME,TYPE,SCHED,ROTA,DISC-GRAN,DISC-MAX KNAME TYPE SCHED ROTA DISC-GRAN DISC-MAX sr0 rom deadline 1 0B 0B vda disk deadline 1 0B 0B vda1 part deadline 1 0B 0B vda2 part deadline 1 0B 0B dm-0 lvm 1 0B 0B dm-1 lvm 1 0B 0B OpenSUSE 13.1: # lsblk -io KNAME,TYPE,SCHED,ROTA,DISC-GRAN,DISC-MAX KNAME TYPE SCHED ROTA DISC-GRAN DISC-MAX sr0 rom cfq 1 0B 0B vda disk cfq 1 0B 0B vda1 part cfq 1 0B 0B vda2 part cfq 1 0B 0B dm-0 lvm 1 0B 0B dm-1 lvm 1 0B 0B Indeed, checking elevator capabilities for boot disk on Ubuntu KVM guest showed: # cat /sys/block/vda/queue/scheduler none Other Linux distributions show more options: # cat /sys/block/vda/queue/scheduler noop deadline [cfq] As well, attempts to change the elevator on Ubuntu guest fail. For example: # echo noop > /sys/block/vda/queue/scheduler # echo $? 0 # cat /sys/block/vda/queue/scheduler none Setting it globally in /etc/default/grub and updating it via update- grub2 fails too. In the meantime, to automate check of elevators (schedulers) and discard support for SSD drives and thin-provisioned volumes on Linux, I wrote simple Perl script: http://www.circlingcycle.com.au/Unix-sources/Linux-check-IO-scheduler- and-discard-support.pl.txt Part of the results on RHEL 6.5 server would look like: INFO: I/O elevator (scheduler) and discard support summary INFO: Hard Disk sdb configured with I/O scheduler "cfq" INFO: SSD sda configured with I/O scheduler "deadline" supports discard operation INFO: Hard Disk sdc configured with I/O scheduler "cfq" INFO: Hard Disk sdi configured with I/O scheduler "cfq" INFO: Hard Disk sdh configured with I/O scheduler "cfq" The Ubuntu KVM guest runs latest paches: Linux ubuntu14-vm2.circlingcycle.com.au 3.13.0-24-generic #47-Ubuntu SMP Fri May 2 23:30:00 UTC 2014 x86_64 x86_64 x86_64 GNU/Linux Regards, Dusan Baljevic VK2COT To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1346687/+subscriptions -- Mailing list: https://launchpad.net/~kernel-packages Post to : kernel-packages@lists.launchpad.net Unsubscribe : https://launchpad.net/~kernel-packages More help : https://help.launchpad.net/ListHelp
