[libvirt PATCH 1/2] qemu: support kvm-poll-control performance hint

[Michal Privoznik]

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 at redhat.com>
> ---
>   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