Re: [RFC PATCH v2] qemu: Use virtio-pci by default for mach-virt guests

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On 10/24/2016 11:28 AM, Andrea Bolognani wrote:

virtio-pci is the way forward for aarch64 guests: it's faster
and less alien to people coming from other architectures.
Now that guest support is finally getting there, we'd like to
start using it by default instead of virtio-mmio.

Users and applications can already opt-in by explicitly using

   <address type='pci'/>

inside the relevant elements, but that's kind of cumbersome and
requires all users and management applications to adapt, which
we'd really like to avoid.

What we can do instead is use virtio-mmio only if the guest
already has at least one virtio-mmio device, and use virtio-pci
in all other situations.

That means existing virtio-mmio guests will keep using the old
addressing scheme, and new guests will automatically be created
using virtio-pci instead. Users can still override the default
in either direction.
---
RFC: still needs polish (documentation, test cases) before it
can be considered for merging, plus it builds on top of changes
that haven't made it into master yet.

Changes from v1:

   * use virDomainDeviceInfoIterate(), as suggested by Martin
     and Laine, which results in cleaner and more robust code

  src/qemu/qemu_domain_address.c                     | 39 ++++++++++++++++++++--
  ...l2argv-aarch64-virt-2.6-virtio-pci-default.args | 14 +++++---
  .../qemuxml2argv-aarch64-virtio-pci-default.args   | 14 +++++---
  .../qemuxml2xmlout-aarch64-virtio-pci-default.xml  | 24 ++++++++++---
  4 files changed, 73 insertions(+), 18 deletions(-)

diff --git a/src/qemu/qemu_domain_address.c b/src/qemu/qemu_domain_address.c
index f27d1e3..30b1ddf 100644
--- a/src/qemu/qemu_domain_address.c
+++ b/src/qemu/qemu_domain_address.c
@@ -386,6 +386,32 @@ qemuDomainAssignS390Addresses(virDomainDefPtr def,
  }
+static int 
+qemuDomainCountVirtioMMIODevicesCallback(virDomainDefPtr def ATTRIBUTE_UNUSED,
+                                         virDomainDeviceDefPtr dev ATTRIBUTE_UNUSED,
+                                         virDomainDeviceInfoPtr info,
+                                         void *opaque)
+{
+    if (info->type == VIR_DOMAIN_DEVICE_ADDRESS_TYPE_VIRTIO_MMIO)
+        (*((size_t *) opaque))++;
(For some reason I had believed that info could be NULL, and had written one of my own callback functions accordingly, but I doublechecked the function that calls this callback and verified that info is always valid.)
A small optimization (that you may not want to make, since you're only doing this once) would be to return -1 when type == MMIO - this causes the iterate to end early. The function would then be less generally useful, though (and you would probably want to rename it accordingly, since it would only ever return 0 or 1).
Another optimization would be to force it to return count == 0 as soon as it encountered any pci address (since the two are mutually exclusive - unless we hav allowed manually mixing them in the past, or maybe it has happened "accidentally" due to libvirt auto-adding a dmi-to-pci-bridge in some older version of libvirt.). If you made such an optimization, you would again probably want the function named differently though - maybe if could be called qemuDomainDetermineDefaultAddressType(), and would return a VIR_DOMAIN_DEVICE_ADDRESS_TYPE_*
All that is purely speculative though - what you have here works just fine and takes an insignificant time to execute relative to everything else that has to happen :-) 



+    return 0;
+}
+
+
+static size_t
+qemuDomainCountVirtioMMIODevices(virDomainDefPtr def)
+{
+    size_t count = 0;
+
+    virDomainDeviceInfoIterate(def,
+                               qemuDomainCountVirtioMMIODevicesCallback,
+                               &count);
+
+    return count;
+}
+
+
  static void
  qemuDomainAssignARMVirtioMMIOAddresses(virDomainDefPtr def,
                                         virQEMUCapsPtr qemuCaps)
@@ -398,9 +424,16 @@ qemuDomainAssignARMVirtioMMIOAddresses(virDomainDefPtr def,
            qemuDomainMachineIsVirt(def)))
          return;
- if (virQEMUCapsGet(qemuCaps, QEMU_CAPS_DEVICE_VIRTIO_MMIO)) { 
-        qemuDomainPrimeVirtioDeviceAddresses(
-            def, VIR_DOMAIN_DEVICE_ADDRESS_TYPE_VIRTIO_MMIO);
+    /* We use virtio-mmio by default on mach-virt guests only if they already
+     * have at least one virtio-mmio device: in all other cases, we prefer
+     * virtio-pci */
+    if (qemuDomainMachineHasPCIeRoot(def) &&
+        qemuDomainCountVirtioMMIODevices(def) == 0) {
+        qemuDomainPrimeVirtioDeviceAddresses(def,
+                                             VIR_DOMAIN_DEVICE_ADDRESS_TYPE_PCI);
+    } else if (virQEMUCapsGet(qemuCaps, QEMU_CAPS_DEVICE_VIRTIO_MMIO)) {
+        qemuDomainPrimeVirtioDeviceAddresses(def,
+                                             VIR_DOMAIN_DEVICE_ADDRESS_TYPE_VIRTIO_MMIO);
      }
  }
diff --git a/tests/qemuxml2argvdata/qemuxml2argv-aarch64-virt-2.6-virtio-pci-default.args b/tests/qemuxml2argvdata/qemuxml2argv-aarch64-virt-2.6-virtio-pci-default.args 
index 75db1a4..df03c6e 100644
--- a/tests/qemuxml2argvdata/qemuxml2argv-aarch64-virt-2.6-virtio-pci-default.args
+++ b/tests/qemuxml2argvdata/qemuxml2argv-aarch64-virt-2.6-virtio-pci-default.args
@@ -21,14 +21,18 @@ QEMU_AUDIO_DRV=none \
  -initrd /aarch64.initrd \
  -append 'earlyprintk console=ttyAMA0,115200n8 rw root=/dev/vda rootwait' \
  -dtb /aarch64.dtb \
--device virtio-serial-device,id=virtio-serial0 \
+-device i82801b11-bridge,id=pci.1,bus=pcie.0,addr=0x1 \
+-device pci-bridge,chassis_nr=2,id=pci.2,bus=pci.1,addr=0x0 \
+-device ioh3420,port=0x10,chassis=3,id=pci.3,bus=pcie.0,addr=0x2 \
+-device virtio-serial-pci,id=virtio-serial0,bus=pci.2,addr=0x2 \
  -drive file=/aarch64.raw,format=raw,if=none,id=drive-virtio-disk0 \
--device virtio-blk-device,drive=drive-virtio-disk0,id=virtio-disk0 \
--device virtio-net-device,vlan=0,id=net0,mac=52:54:00:09:a4:37 \
+-device virtio-blk-pci,bus=pci.2,addr=0x3,drive=drive-virtio-disk0,\
+id=virtio-disk0 \
+-device virtio-net-pci,vlan=0,id=net0,mac=52:54:00:09:a4:37,bus=pci.2,addr=0x1 \
  -net user,vlan=0,name=hostnet0 \
  -serial pty \
  -chardev pty,id=charconsole1 \
  -device virtconsole,chardev=charconsole1,id=console1 \
--device virtio-balloon-device,id=balloon0 \
+-device virtio-balloon-pci,id=balloon0,bus=pci.2,addr=0x4 \
  -object rng-random,id=objrng0,filename=/dev/random \
--device virtio-rng-device,rng=objrng0,id=rng0
+-device virtio-rng-pci,rng=objrng0,id=rng0,bus=pci.2,addr=0x5
diff --git a/tests/qemuxml2argvdata/qemuxml2argv-aarch64-virtio-pci-default.args b/tests/qemuxml2argvdata/qemuxml2argv-aarch64-virtio-pci-default.args
index b5b010c..f205d9a 100644
--- a/tests/qemuxml2argvdata/qemuxml2argv-aarch64-virtio-pci-default.args
+++ b/tests/qemuxml2argvdata/qemuxml2argv-aarch64-virtio-pci-default.args
@@ -21,14 +21,18 @@ QEMU_AUDIO_DRV=none \
  -initrd /aarch64.initrd \
  -append 'earlyprintk console=ttyAMA0,115200n8 rw root=/dev/vda rootwait' \
  -dtb /aarch64.dtb \
--device virtio-serial-device,id=virtio-serial0 \
+-device i82801b11-bridge,id=pci.1,bus=pcie.0,addr=0x1 \
+-device pci-bridge,chassis_nr=2,id=pci.2,bus=pci.1,addr=0x0 \
+-device ioh3420,port=0x10,chassis=3,id=pci.3,bus=pcie.0,addr=0x2 \
+-device virtio-serial-pci,id=virtio-serial0,bus=pci.2,addr=0x2 \
  -drive file=/aarch64.raw,format=raw,if=none,id=drive-virtio-disk0 \
--device virtio-blk-device,drive=drive-virtio-disk0,id=virtio-disk0 \
--device virtio-net-device,vlan=0,id=net0,mac=52:54:00:09:a4:37 \
+-device virtio-blk-pci,bus=pci.2,addr=0x3,drive=drive-virtio-disk0,\
+id=virtio-disk0 \
+-device virtio-net-pci,vlan=0,id=net0,mac=52:54:00:09:a4:37,bus=pci.2,addr=0x1 \
  -net user,vlan=0,name=hostnet0 \
  -serial pty \
  -chardev pty,id=charconsole1 \
  -device virtconsole,chardev=charconsole1,id=console1 \
--device virtio-balloon-device,id=balloon0 \
+-device virtio-balloon-pci,id=balloon0,bus=pci.2,addr=0x4 \
  -object rng-random,id=objrng0,filename=/dev/random \
--device virtio-rng-device,rng=objrng0,id=rng0
+-device virtio-rng-pci,rng=objrng0,id=rng0,bus=pci.2,addr=0x5
diff --git a/tests/qemuxml2xmloutdata/qemuxml2xmlout-aarch64-virtio-pci-default.xml b/tests/qemuxml2xmloutdata/qemuxml2xmlout-aarch64-virtio-pci-default.xml
index 7c3fc19..90659a1 100644
--- a/tests/qemuxml2xmloutdata/qemuxml2xmlout-aarch64-virtio-pci-default.xml
+++ b/tests/qemuxml2xmloutdata/qemuxml2xmlout-aarch64-virtio-pci-default.xml
@@ -30,16 +30,30 @@
      <disk type='file' device='disk'>
        <source file='/aarch64.raw'/>
        <target dev='vda' bus='virtio'/>
-      <address type='virtio-mmio'/>
+      <address type='pci' domain='0x0000' bus='0x02' slot='0x03' function='0x0'/>
      </disk>
      <controller type='pci' index='0' model='pcie-root'/>
      <controller type='virtio-serial' index='0'>
-      <address type='virtio-mmio'/>
+      <address type='pci' domain='0x0000' bus='0x02' slot='0x02' function='0x0'/>
+    </controller>
+    <controller type='pci' index='1' model='dmi-to-pci-bridge'>
+      <model name='i82801b11-bridge'/>
+      <address type='pci' domain='0x0000' bus='0x00' slot='0x01' function='0x0'/>
+    </controller>
+    <controller type='pci' index='2' model='pci-bridge'>
+      <model name='pci-bridge'/>
+      <target chassisNr='2'/>
+      <address type='pci' domain='0x0000' bus='0x01' slot='0x00' function='0x0'/>
+    </controller>
+    <controller type='pci' index='3' model='pcie-root-port'>
+      <model name='ioh3420'/>
+      <target chassis='3' port='0x10'/>
+      <address type='pci' domain='0x0000' bus='0x00' slot='0x02' function='0x0'/>
      </controller>
      <interface type='user'>
        <mac address='52:54:00:09:a4:37'/>
        <model type='virtio'/>
-      <address type='virtio-mmio'/>
+      <address type='pci' domain='0x0000' bus='0x02' slot='0x01' function='0x0'/>
      </interface>
      <serial type='pty'>
        <target port='0'/>
@@ -51,11 +65,11 @@
        <target type='virtio' port='1'/>
      </console>
      <memballoon model='virtio'>
-      <address type='virtio-mmio'/>
+      <address type='pci' domain='0x0000' bus='0x02' slot='0x04' function='0x0'/>
      </memballoon>
      <rng model='virtio'>
        <backend model='random'>/dev/random</backend>
-      <address type='virtio-mmio'/>
+      <address type='pci' domain='0x0000' bus='0x02' slot='0x05' function='0x0'/>
      </rng>
    </devices>
  </domain>
I guess I can agree with keeping this test case as is. It would be nice to have another test that used the identical input file (via symlink) but had the extra flags defined (but it's not needed in this patch). Too bad I didn't think of that as a test case for the patches that changed the behavior for virtio devices (and also that I don't feel like adding it now :-P) 


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