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From 939d57ef4d5bcfa31e9b98104822962b89572481 Mon Sep 17 00:00:00 2001
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From: "Richard W.M. Jones" <rjones@redhat.com>
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Date: Tue, 19 May 2020 14:40:01 +0100
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Subject: [PATCH] v2v: -o libvirt: Remove cache=none (RHBZ#1837453).
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Traditionally if you did live migration (KVM to KVM), you had to
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ensure that cache=none was set on all disks of the guest up front.
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This was because of quirks in how NFS works (I think the close-to-open
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consistency and the fact that during live migration both qemus have
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the file open), and we had to assume the worst case that a guest might
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be backed by NFS.
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Because of this when virt-v2v converts a guest to run on KVM using
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libvirt it sets cache=none.
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This is not necessary with modern qemu. If qemu supports the
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drop-cache property of the file block driver, which libvirt will
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automatically detect for us, then libvirt live migration is able to
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tell qemu to drop cached data at the right time even if the backing is
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NFS.
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It also had a significant performance impact. In some synthetic
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benchmarks it could show 2 or 3 times slower performance.
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Thanks: Ming Xie, Peter Krempa.
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(cherry picked from commit 9720f45e0cd9283739fd2a67c19e66912489dfc7)
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---
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docs/virt-v2v-output-local.pod | 2 +-
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tests/test-v2v-cdrom.expected | 2 +-
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tests/test-v2v-floppy.expected | 2 +-
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tests/test-v2v-i-ova.xml | 2 +-
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v2v/create_libvirt_xml.ml | 1 -
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5 files changed, 4 insertions(+), 5 deletions(-)
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diff --git a/docs/virt-v2v-output-local.pod b/docs/virt-v2v-output-local.pod
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index 38df007d..a5f155cb 100644
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--- a/docs/virt-v2v-output-local.pod
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+++ b/docs/virt-v2v-output-local.pod
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@@ -127,7 +127,7 @@ Edit F to change F to the pool
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name. In other words, locate the following bit of XML:
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<disk type='file' device='disk'>
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- <driver name='qemu' type='raw' cache='none' />
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+ <driver name='qemu' type='raw' />
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<source file='/var/tmp/NAME-sda' />
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<target dev='hda' bus='ide' />
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</disk>
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diff --git a/tests/test-v2v-cdrom.expected b/tests/test-v2v-cdrom.expected
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index e18ea6f2..34d2bf59 100644
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--- a/tests/test-v2v-cdrom.expected
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+++ b/tests/test-v2v-cdrom.expected
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@@ -1,5 +1,5 @@
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<disk type='file' device='disk'>
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- <driver name='qemu' type='raw' cache='none'/>
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+ <driver name='qemu' type='raw'/>
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<target dev='vda' bus='virtio'/>
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</disk>
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<disk device='cdrom' type='file'>
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diff --git a/tests/test-v2v-floppy.expected b/tests/test-v2v-floppy.expected
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index dd74ed94..a718c21f 100644
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--- a/tests/test-v2v-floppy.expected
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+++ b/tests/test-v2v-floppy.expected
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@@ -1,5 +1,5 @@
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<disk type='file' device='disk'>
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- <driver name='qemu' type='raw' cache='none'/>
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+ <driver name='qemu' type='raw'/>
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<target dev='vda' bus='virtio'/>
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</disk>
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<disk device='floppy' type='file'>
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diff --git a/tests/test-v2v-i-ova.xml b/tests/test-v2v-i-ova.xml
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index 7c198283..e26f4f83 100644
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--- a/tests/test-v2v-i-ova.xml
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+++ b/tests/test-v2v-i-ova.xml
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@@ -22,7 +22,7 @@
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<on_crash>restart</on_crash>
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<devices>
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<disk type='file' device='disk'>
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- <driver name='qemu' type='raw' cache='none'/>
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+ <driver name='qemu' type='raw'/>
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<source file='TestOva-sda'/>
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<target dev='vda' bus='virtio'/>
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</disk>
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diff --git a/v2v/create_libvirt_xml.ml b/v2v/create_libvirt_xml.ml
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index 05553c4f..5a1fba0f 100644
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--- a/v2v/create_libvirt_xml.ml
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+++ b/v2v/create_libvirt_xml.ml
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@@ -336,7 +336,6 @@ let create_libvirt_xml ?pool source targets target_buses guestcaps
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e "driver" [
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"name", "qemu";
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"type", t.target_format;
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- "cache", "none"
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] [];
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(match pool with
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| None ->
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--
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2.27.0
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