On 11/13/20 9:49 AM, Tim Wiederhake wrote:
QEMU version 4.2 introduced a performance feature under commit
d645e13287 ("kvm: i386: halt poll control MSR support").
This patch adds a new KVM feature 'poll-control' to set this performance
hint for KVM guests. The feature is off by default.
To enable this hint and have libvirt add "-cpu host,kvm-poll-control=on"
to the QEMU command line, the following XML code needs to be added to the
guest's domain description:
<features>
<kvm>
<poll-control state='on'/>
</kvm>
</features>
Signed-off-by: Tim Wiederhake <twiederh@xxxxxxxxxx>
---
docs/formatdomain.rst | 14 ++++++++------
docs/schemas/domaincommon.rng | 5 +++++
src/conf/domain_conf.c | 4 ++++
src/conf/domain_conf.h | 1 +
src/qemu/qemu_command.c | 5 +++++
5 files changed, 23 insertions(+), 6 deletions(-)
diff --git a/docs/formatdomain.rst b/docs/formatdomain.rst
index a6ab845f92..cd5d7aae56 100644
--- a/docs/formatdomain.rst
+++ b/docs/formatdomain.rst
@@ -1766,6 +1766,7 @@ Hypervisors may allow certain CPU / machine features to be toggled on/off.
<kvm>
<hidden state='on'/>
<hint-dedicated state='on'/>
+ <poll-control='on'/>
</kvm>
<xen>
<e820_host state='on'/>
@@ -1848,12 +1849,13 @@ 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)`
- ============== ====================================================================== ======= ============================
+ ============== ============================================================================ ======= ============================
+ 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:`6.11.0 (QEMU 4.2)`
+ ============== ============================================================================ ======= ============================
Small nit, the next version is 6.10.0 ;-)
Michal
