Re: [Qemu-devel] [PATCH] pc: Fix max_cpus

["Andreas Färber" <afaerber@suse.de>]

Am 23.07.2012 12:47, schrieb riegamaths@gmail.com:
> From: Dunrong Huang <riegamaths@gmail.com>
> 
> The VCPU count limit in kernel now is 254, defined by KVM_MAX_VCPUS
> in kernel's header files. But the count limit in QEMU is 255,
> so QEMU will failed to start if user passes "-enable-kvm" and "-smp 255"
> to it.
> 
> This patch intruduces a Macro MAX_VCPUS whose value is KVM_MAX_VCPUS
> if CONFIG_KVM is defined. If user do not use kvm, set it's value to 255.
> 
> Signed-off-by: Dunrong Huang <riegamaths@gmail.com>
> ---
>  hw/pc_piix.c |   28 +++++++++++++++++++---------
>  1 files changed, 19 insertions(+), 9 deletions(-)
> 
> diff --git a/hw/pc_piix.c b/hw/pc_piix.c
> index 0c0096f..49cda51 100644
> --- a/hw/pc_piix.c
> +++ b/hw/pc_piix.c
> @@ -49,6 +49,16 @@
>  
>  #define MAX_IDE_BUS 2
>  
> +#ifndef KVM_MAX_VCPUS
> +#define KVM_MAX_VCPUS 254
> +#endif
> +
> +#ifdef CONFIG_KVM
> +#define MAX_VCPUS KVM_MAX_VCPUS
> +#else
> +#define MAX_VCPUS 255
> +#endif
> +
>  static const int ide_iobase[MAX_IDE_BUS] = { 0x1f0, 0x170 };
>  static const int ide_iobase2[MAX_IDE_BUS] = { 0x3f6, 0x376 };
>  static const int ide_irq[MAX_IDE_BUS] = { 14, 15 };
> @@ -354,7 +364,7 @@ static QEMUMachine pc_machine_v1_2 = {
>      .alias = "pc",
>      .desc = "Standard PC",
>      .init = pc_init_pci,
> -    .max_cpus = 255,
> +    .max_cpus = MAX_VCPUS,
>      .is_default = 1,
>  };
>  
[snip]

This is not so ideal: -enable-kvm is a runtime switch whereas you are
changing a compile-time limit here. Any chance to change the runtime
usage of .max_cpus instead? Possibly introducing a helper function?

Andreas

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