On 22/08/2013, at 12:39, Andrew Jones <drjones@xxxxxxxxxx> wrote:
> The comment in kvm_max_vcpus() states that it's using the recommended
> procedure from the kernel API documentation to get the max number
> of vcpus that kvm supports. It is, but by always returning the
> maximum number supported. The maximum number should only be used
> for development purposes. qemu should check KVM_CAP_NR_VCPUS for
> the recommended number of vcpus. This patch adds a warning if a user
> specifies a number of cpus between the recommended and max.
>
> Signed-off-by: Andrew Jones <drjones@xxxxxxxxxx>
CCing libvir-list. It is probably interesting for libvirt to expose or warn about the recommended VCPU limit somehow, and in this case a simple warning on stderr won't be enough.
> ---
> kvm-all.c | 45 +++++++++++++++++++++++++++------------------
> 1 file changed, 27 insertions(+), 18 deletions(-)
>
> diff --git a/kvm-all.c b/kvm-all.c
> index 716860f617455..9092e13ae60ea 100644
> --- a/kvm-all.c
> +++ b/kvm-all.c
> @@ -1313,24 +1313,24 @@ static int kvm_irqchip_create(KVMState *s)
> return 0;
> }
>
> -static int kvm_max_vcpus(KVMState *s)
> +/* Find number of supported CPUs using the recommended
> + * procedure from the kernel API documentation to cope with
> + * older kernels that may be missing capabilities.
> + */
> +static int kvm_recommended_vcpus(KVMState *s)
> {
> int ret;
>
> - /* Find number of supported CPUs using the recommended
> - * procedure from the kernel API documentation to cope with
> - * older kernels that may be missing capabilities.
> - */
> - ret = kvm_check_extension(s, KVM_CAP_MAX_VCPUS);
> - if (ret) {
> - return ret;
> - }
> ret = kvm_check_extension(s, KVM_CAP_NR_VCPUS);
> - if (ret) {
> - return ret;
> - }
> + return (ret) ? ret : 4;
> +}
>
> - return 4;
> +static int kvm_max_vcpus(KVMState *s)
> +{
> + int ret;
> +
> + ret = kvm_check_extension(s, KVM_CAP_MAX_VCPUS);
> + return (ret) ? ret : kvm_recommended_vcpus(s);
> }
>
> int kvm_init(void)
> @@ -1383,12 +1383,21 @@ int kvm_init(void)
> goto err;
> }
>
> - max_vcpus = kvm_max_vcpus(s);
> + max_vcpus = kvm_recommended_vcpus(s);
> if (smp_cpus > max_vcpus) {
> - ret = -EINVAL;
> - fprintf(stderr, "Number of SMP cpus requested (%d) exceeds max cpus "
> - "supported by KVM (%d)\n", smp_cpus, max_vcpus);
> - goto err;
> + fprintf(stderr,
> + "Warning: Number of SMP cpus requested (%d) exceeds "
> + "recommended cpus supported by KVM (%d)\n",
> + smp_cpus, max_vcpus);
> +
> + max_vcpus = kvm_max_vcpus(s);
> + if (smp_cpus > max_vcpus) {
> + ret = -EINVAL;
> + fprintf(stderr, "Number of SMP cpus requested (%d) exceeds "
> + "max cpus supported by KVM (%d)\n",
> + smp_cpus, max_vcpus);
> + goto err;
> + }
> }
>
> s->vmfd = kvm_ioctl(s, KVM_CREATE_VM, 0);
> --
> 1.8.1.4
>
--
Eduardo
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