QEMU introduced a CPU power management feature with commit 6f131f13e68d
("kvm: support -overcommit cpu-pm=on|off").

With this flag, kvm allows guest to control host CPU power state.  This
increases latency for other processes using same host CPU in an
unpredictable way, but if decreases idle entry/exit times for the
running VCPU, so to use it QEMU needs a hint about whether host CPU is
overcommitted, hence the flag name.

This patch series adds a new kvm feature 'cpu-pm' for controlling
"-overcommit cpu-pm=[on|off]"

    <features>
      <kvm>
        <cpu-pm state='on'/>
      </kvm>
    </features>


Menno Lageman (2):
  qemu: introduce qemuBuildOvercommitCommandLine()
  tests: add tests for cpu-pm feature

Wim ten Have (1):
  qemu: add hypervisor feature cpu-pm support for kvm

 docs/formatdomain.html.in                     |  7 ++++
 docs/schemas/domaincommon.rng                 |  5 +++
 src/conf/domain_conf.c                        |  4 ++
 src/conf/domain_conf.h                        |  1 +
 src/libvirt_private.syms                      |  1 +
 src/qemu/qemu_command.c                       | 39 +++++++++++++++++--
 src/qemu/qemu_domain.c                        | 25 ++++++++----
 tests/qemuxml2argvdata/kvm-features-off.args  |  2 +-
 tests/qemuxml2argvdata/kvm-features-off.xml   |  1 +
 tests/qemuxml2argvdata/kvm-features.args      |  2 +-
 tests/qemuxml2argvdata/kvm-features.xml       |  1 +
 tests/qemuxml2argvtest.c                      |  4 +-
 tests/qemuxml2xmloutdata/kvm-features-off.xml |  1 +
 tests/qemuxml2xmloutdata/kvm-features.xml     |  1 +
 14 files changed, 79 insertions(+), 15 deletions(-)

-- 
2.21.0

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On Mon, Aug 19, 2019 at 10:32:23AM +0200, Menno Lageman wrote:
> QEMU introduced a CPU power management feature with commit 6f131f13e68d
> ("kvm: support -overcommit cpu-pm=on|off").
> 
> With this flag, kvm allows guest to control host CPU power state.  This
> increases latency for other processes using same host CPU in an
> unpredictable way, but if decreases idle entry/exit times for the
> running VCPU, so to use it QEMU needs a hint about whether host CPU is
> overcommitted, hence the flag name.
> 
> This patch series adds a new kvm feature 'cpu-pm' for controlling
> "-overcommit cpu-pm=[on|off]"
> 
>     <features>
>       <kvm>
>         <cpu-pm state='on'/>
>       </kvm>
>     </features>

Unless I'm missing it, there was never a followup v2 for this
series ?  Did you ever do more work on this, as this is still
a useful feature to support for KVM to maximize performance
AFAIK.


Regards,
Daniel
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On 26-03-2020 17:04, Daniel P. Berrangé wrote:
> On Mon, Aug 19, 2019 at 10:32:23AM +0200, Menno Lageman wrote:
>> QEMU introduced a CPU power management feature with commit 6f131f13e68d
>> ("kvm: support -overcommit cpu-pm=on|off").
>>
>> With this flag, kvm allows guest to control host CPU power state.  This
>> increases latency for other processes using same host CPU in an
>> unpredictable way, but if decreases idle entry/exit times for the
>> running VCPU, so to use it QEMU needs a hint about whether host CPU is
>> overcommitted, hence the flag name.
>>
>> This patch series adds a new kvm feature 'cpu-pm' for controlling
>> "-overcommit cpu-pm=[on|off]"
>>
>>      <features>
>>        <kvm>
>>          <cpu-pm state='on'/>
>>        </kvm>
>>      </features>
> 
> Unless I'm missing it, there was never a followup v2 for this
> series ?  Did you ever do more work on this, as this is still
> a useful feature to support for KVM to maximize performance
> AFAIK.
> 

It's on my TODO list but other things got ahead in the queue.

Menno