Re: [Qemu-devel] [PATCH v2 1/2] kvm: support -realtime cpu-pm=on|off

[Eduardo Habkost <ehabkost@redhat.com>]

On Tue, Jun 12, 2018 at 09:47:11PM +0300, Michael S. Tsirkin wrote:
> 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.
> 
> Follow-up patches will expose this capability to guest
> (using mwait leaf).
> 
> Based on a patch by Wanpeng Li <kernellwp@gmail.com> .
> 
> Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
> ---
>  include/sysemu/sysemu.h |  1 +
>  target/i386/kvm.c       | 22 ++++++++++++++++++++++
>  vl.c                    |  6 ++++++
>  qemu-options.hx         |  9 +++++++--
>  4 files changed, 36 insertions(+), 2 deletions(-)
> 
> diff --git a/include/sysemu/sysemu.h b/include/sysemu/sysemu.h
> index e893f72f3b..b921c6f3b7 100644
> --- a/include/sysemu/sysemu.h
> +++ b/include/sysemu/sysemu.h
> @@ -128,6 +128,7 @@ extern bool boot_strict;
>  extern uint8_t *boot_splash_filedata;
>  extern size_t boot_splash_filedata_size;
>  extern bool enable_mlock;
> +extern bool enable_cpu_pm;

After looking at patch 2/2, I see that the global variable is
useful, and it's consistent with the existing enable_mlock
variable.

>  extern uint8_t qemu_extra_params_fw[2];
>  extern QEMUClockType rtc_clock;
>  extern const char *mem_path;
> diff --git a/target/i386/kvm.c b/target/i386/kvm.c
> index 44f70733e7..f093d55209 100644
> --- a/target/i386/kvm.c
> +++ b/target/i386/kvm.c
> @@ -1357,6 +1357,28 @@ int kvm_arch_init(MachineState *ms, KVMState *s)
>          smram_machine_done.notify = register_smram_listener;
>          qemu_add_machine_init_done_notifier(&smram_machine_done);
>      }
> +
> +    if (enable_cpu_pm) {
> +        int disable_exits = kvm_check_extension(s, KVM_CAP_X86_DISABLE_EXITS);
> +        int ret;
> +
> +/* Work around for kernel header with a typo. TODO: fix header and drop. */
> +#if defined(KVM_X86_DISABLE_EXITS_HTL) && !defined(KVM_X86_DISABLE_EXITS_HLT)
> +#define KVM_X86_DISABLE_EXITS_HLT KVM_X86_DISABLE_EXITS_HTL
> +#endif
> +        if (disable_exits) {
> +            disable_exits &= (KVM_X86_DISABLE_EXITS_MWAIT |
> +                              KVM_X86_DISABLE_EXITS_HLT |
> +                              KVM_X86_DISABLE_EXITS_PAUSE);
> +        }
> +
> +        ret = kvm_vm_enable_cap(s, KVM_CAP_X86_DISABLE_EXITS, 0,
> +                                disable_exits);

Isn't the kvm_vm_enable_cap() call supposed to be inside the "if
(disable_exits)" block?

> +        if (ret < 0) {
> +            error_report("kvm: guest stopping CPU not supported: %s", strerror(-ret));
> +        }
> +    }
> +
>      return 0;
>  }
[...]

-- 
Eduardo