[Qemu-devel] [Bug 1483070] [NEW] VIRTIO Sequential Write IOPS limits not working

[James Watson]

Public bug reported:

Root Problem:
IOPS limit does not work for VIRTIO devices if the disk workload is a 
sequential write.

To confirm:
IDE disk devices - the IOPS limit works fine. Disk transfer speed limit works 
fine.
VIRTIO disk devices - the IOPS limit works fine for random IO (write/read) and 
sequential read, but not for sequential write. Disk transfer speed limits work 
fine.

Tested on Windows 7,10 and 2k12 (Fedora drivers used and here is the twist):
virtio-win-0.1.96 (stable) or older won't limit write IO if workload is 
sequential.
virtio-win-0.1.105 (latest) or newer will limit but I have had two test 
machines crash when under high workload using IOPS limit.

For Linux:
The issue is also apparent, tested on Ubuntu 14.04

On the hypervisor (using KVM) machine I have tried with Qemu 2.1.2
(3.16.0-4-amd64 - Debian 8) and Qemu 2.3.0 (3.19.8-1-pve - Proxmox 3.4
and 4) using multiple machines but all are 64bit intel.

Even though the latest VIRTIO guest drivers fix the problem, the guest
drivers shouldn't be able to ignore the limits the host puts in place or
am I missing something??

** Affects: qemu
     Importance: Undecided
         Status: New


** Tags: iops limits sequential virtio write

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https://bugs.launchpad.net/bugs/1483070

Title:
  VIRTIO Sequential Write IOPS limits not working

Status in QEMU:
  New

Bug description:
  Root Problem:
  IOPS limit does not work for VIRTIO devices if the disk workload is a 
sequential write.

  To confirm:
  IDE disk devices - the IOPS limit works fine. Disk transfer speed limit works 
fine.
  VIRTIO disk devices - the IOPS limit works fine for random IO (write/read) 
and sequential read, but not for sequential write. Disk transfer speed limits 
work fine.

  Tested on Windows 7,10 and 2k12 (Fedora drivers used and here is the twist):
  virtio-win-0.1.96 (stable) or older won't limit write IO if workload is 
sequential.
  virtio-win-0.1.105 (latest) or newer will limit but I have had two test 
machines crash when under high workload using IOPS limit.

  For Linux:
  The issue is also apparent, tested on Ubuntu 14.04

  On the hypervisor (using KVM) machine I have tried with Qemu 2.1.2
  (3.16.0-4-amd64 - Debian 8) and Qemu 2.3.0 (3.19.8-1-pve - Proxmox 3.4
  and 4) using multiple machines but all are 64bit intel.

  Even though the latest VIRTIO guest drivers fix the problem, the guest
  drivers shouldn't be able to ignore the limits the host puts in place
  or am I missing something??

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