PING: [PATCH] qemu: support kvm-pv-ipi off

[zhenwei pi]

PING

On 10/27/21 3:04 PM, zhenwei pi wrote:
> QEMU version 3.1 introduced PV_SEND_IPI CPUID feature bit under
> commit 7f710c32bb8 (target-i386: adds PV_SEND_IPI CPUID feature bit).
> 
> This patch adds a new KVM feature 'pv-ipi' to disable this feature
> (enabled by default). Newer CPU platform (Ex, AMD Zen2) supports
> hardware accelation for IPI in guest, to use this feature to get
> better performance in some scenarios. Detailed about the discussion:
>    https://lkml.org/lkml/2021/10/20/423
> 
> To disable kvm-pv-ipi and have libvirt add "-cpu host,kvm-pv-ipi=off"
> to the QEMU command line, the following XML code needs to be added to the
> guest's domain description:
> 
>    <features>
>      <kvm>
>        <pv-ipi state='off'/>
>      </kvm>
>    </features>
> 
> Signed-off-by: zhenwei pi <pizhenwei at bytedance.com>
> ---
>   docs/formatdomain.rst         | 2 ++
>   docs/schemas/domaincommon.rng | 5 +++++
>   src/conf/domain_conf.c        | 3 +++
>   src/conf/domain_conf.h        | 1 +
>   src/qemu/qemu_command.c       | 5 +++++
>   5 files changed, 16 insertions(+)
> 
> diff --git a/docs/formatdomain.rst b/docs/formatdomain.rst
> index 58768f7e5e..8ff833bbd2 100644
> --- a/docs/formatdomain.rst
> +++ b/docs/formatdomain.rst
> @@ -1842,6 +1842,7 @@ Hypervisors may allow certain CPU / machine features to be toggled on/off.
>          <hidden state='on'/>
>          <hint-dedicated state='on'/>
>          <poll-control state='on'/>
> +       <pv-ipi state='off'/>
>        </kvm>
>        <xen>
>          <e820_host state='on'/>
> @@ -1930,6 +1931,7 @@ are:
>      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)`
>      ============== ============================================================================ ======= ============================
>   
>   ``xen``
> diff --git a/docs/schemas/domaincommon.rng b/docs/schemas/domaincommon.rng
> index f71e375a33..67df13d90d 100644
> --- a/docs/schemas/domaincommon.rng
> +++ b/docs/schemas/domaincommon.rng
> @@ -7177,6 +7177,11 @@
>               <ref name="featurestate"/>
>             </element>
>           </optional>
> +        <optional>
> +          <element name="pv-ipi">
> +            <ref name="featurestate"/>
> +          </element>
> +        </optional>
>         </interleave>
>       </element>
>     </define>
> diff --git a/src/conf/domain_conf.c b/src/conf/domain_conf.c
> index 48c6ee9865..c8868de577 100644
> --- a/src/conf/domain_conf.c
> +++ b/src/conf/domain_conf.c
> @@ -204,6 +204,7 @@ VIR_ENUM_IMPL(virDomainKVM,
>                 "hidden",
>                 "hint-dedicated",
>                 "poll-control",
> +              "pv-ipi",
>   );
>   
>   VIR_ENUM_IMPL(virDomainXen,
> @@ -21789,6 +21790,7 @@ virDomainDefFeaturesCheckABIStability(virDomainDef *src,
>               case VIR_DOMAIN_KVM_HIDDEN:
>               case VIR_DOMAIN_KVM_DEDICATED:
>               case VIR_DOMAIN_KVM_POLLCONTROL:
> +            case VIR_DOMAIN_KVM_PVIPI:
>                   if (src->kvm_features[i] != dst->kvm_features[i]) {
>                       virReportError(VIR_ERR_CONFIG_UNSUPPORTED,
>                                      _("State of KVM feature '%s' differs: "
> @@ -27821,6 +27823,7 @@ virDomainDefFormatFeatures(virBuffer *buf,
>                   case VIR_DOMAIN_KVM_HIDDEN:
>                   case VIR_DOMAIN_KVM_DEDICATED:
>                   case VIR_DOMAIN_KVM_POLLCONTROL:
> +                case VIR_DOMAIN_KVM_PVIPI:
>                       if (def->kvm_features[j])
>                           virBufferAsprintf(&childBuf, "<%s state='%s'/>\n",
>                                             virDomainKVMTypeToString(j),
> diff --git a/src/conf/domain_conf.h b/src/conf/domain_conf.h
> index f4be5c84f0..cb6d8975b8 100644
> --- a/src/conf/domain_conf.h
> +++ b/src/conf/domain_conf.h
> @@ -2073,6 +2073,7 @@ typedef enum {
>       VIR_DOMAIN_KVM_HIDDEN = 0,
>       VIR_DOMAIN_KVM_DEDICATED,
>       VIR_DOMAIN_KVM_POLLCONTROL,
> +    VIR_DOMAIN_KVM_PVIPI,
>   
>       VIR_DOMAIN_KVM_LAST
>   } virDomainKVM;
> diff --git a/src/qemu/qemu_command.c b/src/qemu/qemu_command.c
> index 7374b2beca..f7c19246d8 100644
> --- a/src/qemu/qemu_command.c
> +++ b/src/qemu/qemu_command.c
> @@ -6848,6 +6848,11 @@ qemuBuildCpuCommandLine(virCommand *cmd,
>                       virBufferAddLit(&buf, ",kvm-poll-control=on");
>                   break;
>   
> +            case VIR_DOMAIN_KVM_PVIPI:
> +                if (def->kvm_features[i] == VIR_TRISTATE_SWITCH_OFF)
> +                    virBufferAddLit(&buf, ",kvm-pv-ipi=off");
> +                break;
> +
>               case VIR_DOMAIN_KVM_LAST:
>                   break;
>               }
> 

-- 
zhenwei pi