'qemu-img convert' performance regression when target is a LVM volume

Bug #1895487 reported by Fridtjof Mund on 2020-09-14
6
This bug affects 1 person
Affects Status Importance Assigned to Milestone
Ubuntu Cloud Archive
Undecided
Unassigned
Stein
Undecided
Unassigned
qemu (Ubuntu)
Undecided
Unassigned

Bug Description

Running Ubuntu Server 18.04 with the Ubuntu Cloud Archive repository on release 'bionic-updates/stein'

qemu-utils version 1:3.1+dfsg-2ubuntu3.7~cloud0

With bionic-updates/rocky and (stock bionic-updates) qemu-utils version 1:2.11+dfsg-1ubuntu7.31, the following command takes ~35 seconds to complete:

# qemu-img convert -p -O raw -t none -f qcow2 some-qcow2.img /dev/mapper/cinder--volumes-volume--9d18daa7--691c--44bc--b4c8--a60cc70a435d

With bionic-updates/stein and qemu-utils version 1:3.1+dfsg-2ubuntu3.7~cloud0, the same command does not progress visibly (-p displays a rough percentage done), still displaying 0% finished after two minutes.

Basic package level bisecting shows that qemu-utils version 1:4.0+dfsg-0ubuntu9.8~cloud0 (from bionic-updates/train) fixes the regression, behaving like 1:2.11+dfsg-1ubuntu7.31 again.

After verifying the bug also exists upstream, I bisected with the following results:

- The bug was introduced with commit 34fa110e424e9a6a9b7e0274c3d4bfee766eb7ed (between v3.0.0-rc2 and rc3)

- The bug was fixed with commit c9fdcf202f19fc2acdcb1ee0522ff5d61bf8c906 (between v3.1 and v4.0), which is part of this patchset: https://patchwork.kernel.org/cover/10865751/

Thank you Fridtjof, for active Ubuntu releases this is either not present or fixed already:
 qemu | 1:2.5+dfsg-5ubuntu10.45 | xenial-updates | source
 qemu | 1:2.11+dfsg-1ubuntu7.31 | bionic-updates | source
 qemu | 1:4.2-3ubuntu6.4 | focal-updates | source, amd64, arm64, armhf, ppc64el, riscv64, s390x

3.1 was based on Ubuntu Disco (19.04) - But you are right it is present in Stein still, let me help you to re-target the bug accordingly for the Openstack Team to see it.

Changed in qemu (Ubuntu):
status: New → Won't Fix
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