[v2] accel: default to an actually available accelerator

configure_accelerator() falls back to tcg if no accelerator has
been specified. Formerly, we could be sure that tcg is always
available; however, with --disable-tcg, this is not longer true,
and you are not able to start qemu without explicitly specifying
another accelerator on those builds.

Instead, choose an accelerator in the order tcg->kvm->hax.

Signed-off-by: Cornelia Huck <cohuck@redhat.com>
---
RFC->v2:
- drop xen from the list of fallbacks
- use comma-delimited list of accelerators (much easier)
- changed one place in qemu-options.hx that had been missed
---
 accel/accel.c   | 3 +--
 qemu-options.hx | 8 +++++---
 2 files changed, 6 insertions(+), 5 deletions(-)

On 13.09.2017 19:29, Cornelia Huck wrote:
> configure_accelerator() falls back to tcg if no accelerator has
> been specified. Formerly, we could be sure that tcg is always
> available; however, with --disable-tcg, this is not longer true,
> and you are not able to start qemu without explicitly specifying
> another accelerator on those builds.
> 
> Instead, choose an accelerator in the order tcg->kvm->hax.
> 
> Signed-off-by: Cornelia Huck <cohuck@redhat.com>
> ---
> RFC->v2:
> - drop xen from the list of fallbacks
> - use comma-delimited list of accelerators (much easier)
> - changed one place in qemu-options.hx that had been missed
> ---
>  accel/accel.c   | 3 +--
>  qemu-options.hx | 8 +++++---
>  2 files changed, 6 insertions(+), 5 deletions(-)
> 
> diff --git a/accel/accel.c b/accel/accel.c
> index 8ae40e1e13..e8a3121d06 100644
> --- a/accel/accel.c
> +++ b/accel/accel.c
> @@ -79,8 +79,7 @@ void configure_accelerator(MachineState *ms)
>  
>      accel = qemu_opt_get(qemu_get_machine_opts(), "accel");
>      if (accel == NULL) {
> -        /* Use the default "accelerator", tcg */
> -        accel = "tcg";
> +        accel = "tcg:kvm:hax";
>      }
>  
>      p = accel;
> diff --git a/qemu-options.hx b/qemu-options.hx
> index 9f6e2adfff..2ff88389e0 100644
> --- a/qemu-options.hx
> +++ b/qemu-options.hx
> @@ -31,7 +31,7 @@ DEF("machine", HAS_ARG, QEMU_OPTION_machine, \
>      "-machine [type=]name[,prop[=value][,...]]\n"
>      "                selects emulated machine ('-machine help' for list)\n"
>      "                property accel=accel1[:accel2[:...]] selects accelerator\n"
> -    "                supported accelerators are kvm, xen, hax or tcg (default: tcg)\n"
> +    "                supported accelerators are kvm, xen, hax or tcg (default: tcg:kvm:hax)\n"
>      "                kernel_irqchip=on|off|split controls accelerated irqchip support (default=off)\n"
>      "                vmport=on|off|auto controls emulation of vmport (default: auto)\n"
>      "                kvm_shadow_mem=size of KVM shadow MMU in bytes\n"
> @@ -66,7 +66,8 @@ Supported machine properties are:
>  @table @option
>  @item accel=@var{accels1}[:@var{accels2}[:...]]
>  This is used to enable an accelerator. Depending on the target architecture,
> -kvm, xen, hax or tcg can be available. By default, tcg is used. If there is
> +kvm, xen, hax or tcg can be available. By default, the first one available
> +out of tcg, kvm, hax (in that order) is used. If there is
>  more than one accelerator specified, the next one is used if the previous one
>  fails to initialize.
>  @item kernel_irqchip=on|off
> @@ -126,7 +127,8 @@ STEXI
>  @item -accel @var{name}[,prop=@var{value}[,...]]
>  @findex -accel
>  This is used to enable an accelerator. Depending on the target architecture,
> -kvm, xen, hax or tcg can be available. By default, tcg is used. If there is
> +kvm, xen, hax or tcg can be available. By default, the first one available
> +out of tcg, kvm, hax (in that order) is used. If there is
>  more than one accelerator specified, the next one is used if the previous one
>  fails to initialize.
>  @table @option

Reviewed-by: Thomas Huth <thuth@redhat.com>

On 09/13/2017 10:29 AM, Cornelia Huck wrote:
> configure_accelerator() falls back to tcg if no accelerator has
> been specified. Formerly, we could be sure that tcg is always
> available; however, with --disable-tcg, this is not longer true,
> and you are not able to start qemu without explicitly specifying
> another accelerator on those builds.
> 
> Instead, choose an accelerator in the order tcg->kvm->hax.
> 
> Signed-off-by: Cornelia Huck <cohuck@redhat.com>
> ---
> RFC->v2:
> - drop xen from the list of fallbacks
> - use comma-delimited list of accelerators (much easier)
> - changed one place in qemu-options.hx that had been missed

Queued to tcg-next.  Thanks,


r~

On Wed, 13 Sep 2017 11:09:04 -0700
Richard Henderson <richard.henderson@linaro.org> wrote:

> On 09/13/2017 10:29 AM, Cornelia Huck wrote:
> > configure_accelerator() falls back to tcg if no accelerator has
> > been specified. Formerly, we could be sure that tcg is always
> > available; however, with --disable-tcg, this is not longer true,
> > and you are not able to start qemu without explicitly specifying
> > another accelerator on those builds.
> > 
> > Instead, choose an accelerator in the order tcg->kvm->hax.
> > 
> > Signed-off-by: Cornelia Huck <cohuck@redhat.com>
> > ---
> > RFC->v2:
> > - drop xen from the list of fallbacks
> > - use comma-delimited list of accelerators (much easier)
> > - changed one place in qemu-options.hx that had been missed  
> 
> Queued to tcg-next.  Thanks,

Hm, has this fallen through the cracks?