[pve-devel] [PATCH qemu-server] fix #4296: virtio-net: enable packed queues for qemu 7.1

[Alexandre Derumier]

virtio 1.1 have improve virtio multiqueue performance,
with a new implementation called "packed queues".

https://www.redhat.com/en/blog/packed-virtqueue-how-reduce-overhead-virtio
https://archive.fosdem.org/2018/schedule/event/virtio/attachments/slides/2167/export/events/attachments/virtio/slides/2167/fosdem_virtio1_1.pdf

This patch enable it by default for qemu 7.1

This don't break old guests with old virtio 1.0 drivers,
as virtio device/devices are forward/backward compatible.

Signed-off-by: Alexandre Derumier <aderumier at odiso.com>
---
 PVE/QemuServer.pm | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/PVE/QemuServer.pm b/PVE/QemuServer.pm
index 4e85dd0..55451de 100644
--- a/PVE/QemuServer.pm
+++ b/PVE/QemuServer.pm
@@ -1726,7 +1726,7 @@ sub print_pbs_blockdev {
 }
 
 sub print_netdevice_full {
-    my ($vmid, $conf, $net, $netid, $bridges, $use_old_bios_files, $arch, $machine_type) = @_;
+    my ($vmid, $conf, $net, $netid, $bridges, $use_old_bios_files, $arch, $machine_type, $machine_version) = @_;
 
     my $device = $net->{model};
     if ($net->{model} eq 'virtio') {
@@ -1740,6 +1740,9 @@ sub print_netdevice_full {
 	# and out of each queue plus one config interrupt and control vector queue
 	my $vectors = $net->{queues} * 2 + 2;
 	$tmpstr .= ",vectors=$vectors,mq=on";
+	if (min_version($machine_version, 7, 1)) {
+	    $tmpstr .= ",packed=on";
+	}
     }
     $tmpstr .= ",bootindex=$net->{bootindex}" if $net->{bootindex} ;
 
@@ -4017,7 +4020,7 @@ sub config_to_command {
 	push @$devices, '-netdev', $netdevfull;
 
 	my $netdevicefull = print_netdevice_full(
-	    $vmid, $conf, $d, $netname, $bridges, $use_old_bios_files, $arch, $machine_type);
+	    $vmid, $conf, $d, $netname, $bridges, $use_old_bios_files, $arch, $machine_type, $machine_version);
 
 	push @$devices, '-device', $netdevicefull;
     }
@@ -4248,11 +4251,12 @@ sub vm_deviceplug {
 	return if !qemu_netdevadd($vmid, $conf, $arch, $device, $deviceid);
 
 	my $machine_type = PVE::QemuServer::Machine::qemu_machine_pxe($vmid, $conf);
+	my $machine_version = PVE::QemuServer::Machine::extract_version($machine_type);
 	my $use_old_bios_files = undef;
 	($use_old_bios_files, $machine_type) = qemu_use_old_bios_files($machine_type);
 
 	my $netdevicefull = print_netdevice_full(
-	    $vmid, $conf, $device, $deviceid, undef, $use_old_bios_files, $arch, $machine_type);
+	    $vmid, $conf, $device, $deviceid, undef, $use_old_bios_files, $arch, $machine_type, $machine_version);
 	qemu_deviceadd($vmid, $netdevicefull);
 	eval {
 	    qemu_deviceaddverify($vmid, $deviceid);
-- 
2.30.2