Re: [Qemu-devel] [PATCH] kvm: Set default accelerator to "kvm" if the host supports it

[Andreas Färber]

Hello Jan,

Am 01.10.2012 16:34, schrieb Jan Kiszka:
> If we built a target for a host that supports KVM in principle, set the
> default accelerator to KVM as well. This also means the start of QEMU
> will fail to start if KVM support turns out to be unavailable at
> runtime.

>From a distro point of view this of course means that we will build
against KVM and that the new KVM default will start to fail for users on
very old hardware. Can't we do a runtime check to select the default?

Would be nice to at least amend the commit message with how they are
expected to remedy that via command line. -machine accel=tcg?

Regards,
Andreas

> 
> Signed-off-by: Jan Kiszka <address@hidden>
> ---
>  kvm-all.c  |    1 +
>  kvm-stub.c |    1 +
>  kvm.h      |    1 +
>  vl.c       |    4 ++--
>  4 files changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/kvm-all.c b/kvm-all.c
> index 92a7137..4d5f86c 100644
> --- a/kvm-all.c
> +++ b/kvm-all.c
> @@ -103,6 +103,7 @@ struct KVMState
>  #endif
>  };
>  
> +bool kvm_configured = true;
>  KVMState *kvm_state;
>  bool kvm_kernel_irqchip;
>  bool kvm_async_interrupts_allowed;
> diff --git a/kvm-stub.c b/kvm-stub.c
> index 3c52eb5..86a6451 100644
> --- a/kvm-stub.c
> +++ b/kvm-stub.c
> @@ -17,6 +17,7 @@
>  #include "gdbstub.h"
>  #include "kvm.h"
>  
> +bool kvm_configured;
>  KVMState *kvm_state;
>  bool kvm_kernel_irqchip;
>  bool kvm_async_interrupts_allowed;
> diff --git a/kvm.h b/kvm.h
> index dea2998..9936e5f 100644
> --- a/kvm.h
> +++ b/kvm.h
> @@ -22,6 +22,7 @@
>  #include <linux/kvm.h>
>  #endif
>  
> +extern bool kvm_configured;
>  extern int kvm_allowed;
>  extern bool kvm_kernel_irqchip;
>  extern bool kvm_async_interrupts_allowed;
> diff --git a/vl.c b/vl.c
> index 8d305ca..f557bd1 100644
> --- a/vl.c
> +++ b/vl.c
> @@ -2215,8 +2215,8 @@ static int configure_accelerator(void)
>      }
>  
>      if (p == NULL) {
> -        /* Use the default "accelerator", tcg */
> -        p = "tcg";
> +        /* The default accelerator depends on the availability of KVM. */
> +        p = kvm_configured ? "kvm" : "tcg";
>      }
>  
>      while (!accel_initialised && *p != '\0') {
> 


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