Re: [PATCH v6 4/4] qemu: support dirty ring feature

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在 2021/11/22 16:55, Peter Krempa 写道:
On Sat, Nov 20, 2021 at 03:20:48 -0500, huangy81@xxxxxxxxxxxxxxx wrote:
From: Hyman Huang(黄勇) <huangy81@xxxxxxxxxxxxxxx>

dirty ring feature was introduced in qemu-6.1, this patch add
corresponding feature named 'dirty-ring', which enable
dirty ring feature when starting vm.

to enable the feature, libvirt add "-accel dirty-ring-size=xxx"
to QEMU command line, the following XML needs to be added to
the guest's domain description:

<features>
    <kvm>
      <dirty-ring state='on' size='xxx'>
    </kvm>
</features>

if property "state=on" but property "size" not be configured, set
default ring size with 4096.

since dirty ring can only be enabled by specifying "-accel" option
and do not support the legacy style, it seems that there's no
other way to work around this, so we use "-accel" option to specify
accelerator instead of "-machine" when building qemu commandline.

details about the qemu "-accel" option:
https://lore.kernel.org/qemu-devel/3aa73987-40e8-3619-0723-9f17f73850bd@xxxxxxxxxx/

Signed-off-by: Hyman Huang(黄勇) <huangy81@xxxxxxxxxxxxxxx>
---
  docs/formatdomain.rst         | 18 ++++++++++--------
  docs/schemas/domaincommon.rng | 10 ++++++++++
  src/qemu/qemu_command.c       |  6 ++++++
  3 files changed, 26 insertions(+), 8 deletions(-)

diff --git a/docs/formatdomain.rst b/docs/formatdomain.rst
index eb8c973cf1..ea69b61c70 100644
--- a/docs/formatdomain.rst
+++ b/docs/formatdomain.rst
@@ -1843,6 +1843,7 @@ Hypervisors may allow certain CPU / machine features to be toggled on/off.
         <hint-dedicated state='on'/>
         <poll-control state='on'/>
         <pv-ipi state='off'/>
+       <dirty-ring state='on' size='4096'/>
       </kvm>
       <xen>
         <e820_host state='on'/>
@@ -1925,14 +1926,15 @@ are:
  ``kvm``
     Various features to change the behavior of the KVM hypervisor.
- ============== ============================================================================ ======= ============================
-   Feature        Description                                                                  Value   Since
-   ============== ============================================================================ ======= ============================
-   hidden         Hide the KVM hypervisor from standard MSR based discovery                    on, off :since:`1.2.8 (QEMU 2.1.0)`
-   hint-dedicated Allows a guest to enable optimizations when running on dedicated vCPUs       on, off :since:`5.7.0 (QEMU 2.12.0)`
-   poll-control   Decrease IO completion latency by introducing a grace period of busy waiting on, off :since:`6.10.0 (QEMU 4.2)`
-   pv-ipi         Paravirtualized send IPIs                                                    on, off :since:`7.10.0 (QEMU 3.1)`
-   ============== ============================================================================ ======= ============================
+   ============== ============================================================================ ====================================================== ============================
+   Feature        Description                                                                  Value                                                  Since
+   ============== ============================================================================ ====================================================== ============================
+   hidden         Hide the KVM hypervisor from standard MSR based discovery                    on, off                                                :since:`1.2.8 (QEMU 2.1.0)`
+   hint-dedicated Allows a guest to enable optimizations when running on dedicated vCPUs       on, off                                                :since:`5.7.0 (QEMU 2.12.0)`
+   poll-control   Decrease IO completion latency by introducing a grace period of busy waiting on, off                                                :since:`6.10.0 (QEMU 4.2)`
+   pv-ipi         Paravirtualized send IPIs                                                    on, off                                                :since:`7.10.0 (QEMU 3.1)`
+   dirty-ring     Enable dirty ring feature                                                    on, off; size - must be power of 2, range [1024,65536] :since:`7.10.0 (QEMU 6.1)`
+   ============== ============================================================================ ====================================================== ============================
``xen``
     Various features to change the behavior of the Xen hypervisor.

Okay, so both hunks belong actually to the previous commit.

diff --git a/docs/schemas/domaincommon.rng b/docs/schemas/domaincommon.rng
index f01b7a6470..5f9fe3cc58 100644
--- a/docs/schemas/domaincommon.rng
+++ b/docs/schemas/domaincommon.rng
@@ -7212,6 +7212,16 @@
              <ref name="featurestate"/>
            </element>
          </optional>
+        <optional>
+          <element name="dirty-ring">
+            <ref name="featurestate"/>
+            <optional>
+              <attribute name="size">
+                <data type="unsignedInt"/>
+              </attribute>
+            </optional>
+          </element>
+        </optional>
        </interleave>
      </element>
    </define>

And this one too.

Ok, i'll squash into the previous commit
diff --git a/src/qemu/qemu_command.c b/src/qemu/qemu_command.c
index 145596d11a..863876bfae 100644
--- a/src/qemu/qemu_command.c
+++ b/src/qemu/qemu_command.c
@@ -7043,6 +7043,12 @@ qemuBuildAccelCommandLineKvmOptions(virCommand *cmd,
          g_auto(virBuffer) buf = VIR_BUFFER_INITIALIZER;
          virCommandAddArg(cmd, "-accel");
          virBufferAddLit(&buf, "kvm");
+
+        if (def->features[VIR_DOMAIN_FEATURE_KVM] == VIR_TRISTATE_SWITCH_ON &&
+            def->kvm_features[VIR_DOMAIN_KVM_DIRTY_RING] == VIR_TRISTATE_SWITCH_ON) {
+            virBufferAsprintf(&buf, ",dirty-ring-size=%d", def->dirty_ring_size);
+        }
+
          virCommandAddArgBuffer(cmd, &buf);
      }
  }

A test case is needed both for qemuxml2argvtest and qemuxml2xmltest.

Ok, i'll add a commit for test case implementation





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