Re: [PATCH v3] xen/dom0less: support for vcpu affinity

[Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>]

On 2/18/25 9:29 PM, Stefano Stabellini wrote:

> Add vcpu affinity to the dom0less bindings. Example:
>
>     dom1 {
>             ...
>             cpus = <4>;
>             vcpu0 {
>                    compatible = "xen,vcpu-affinity";
>                    id = <0>;
>                    hard-affinity = "4-7";
>             };
>             vcpu1 {
>                    compatible = "xen,vcpu-affinity";
>                    id = <1>;
>                    hard-affinity = "0-3";
>             };
>             vcpu2 {
>                    compatible = "xen,vcpu-affinity";
>                    id = <2>;
>                    hard-affinity = "1,6";
>             };
>             ...
>
> Note that the property hard-affinity is optional. It is possible to add
> other properties in the future not only to specify soft affinity, but
> also to provide more precise methods for configuring affinity. For
> instance, on ARM the MPIDR could be use to specify the pCPU. For now, it
> is left to the future.
>     
I think we want this to add to CHANGELOG.

Thanks.

~ Oleksii

> Signed-off-by: Xenia Ragiadakou <xenia.ragiadakou@xxxxxxx>
> Signed-off-by: Stefano Stabellini <stefano.stabellini@xxxxxxx>
> ---
> Changes in v3:
> - improve commit message
> - improve binding doc
> - add panic on invalid pCPU
> - move parsing to a separate function
>
> diff --git a/docs/misc/arm/device-tree/booting.txt b/docs/misc/arm/device-tree/booting.txt
> index 9c881baccc..10e55c825c 100644
> --- a/docs/misc/arm/device-tree/booting.txt
> +++ b/docs/misc/arm/device-tree/booting.txt
> @@ -324,6 +324,27 @@ The ramdisk sub-node has the following properties:
>      property because it will be created by the UEFI stub on boot.
>      This option is needed only when UEFI boot is used.
>  
> +Under the "xen,domain" compatible node, it is possible optionally to add
> +one or more sub-nodes to configure vCPU affinity. The vCPU affinity
> +sub-node has the following properties:
> +
> +- compatible
> +
> +    "xen,vcpu-affinity"
> +
> +- id
> +
> +    A 32-bit integer that specifies the vCPU id. 0 is the first vCPU.
> +    The last vCPU is cpus-1, where "cpus" is the number of vCPUs
> +    specified with the "cpus" property under the "xen,domain" node.
> +
> +- hard-affinity
> +
> +    Optional. A string specifying the hard affinity configuration for the
> +    vCPU: a comma-separated list of pCPUs or ranges of pCPUs is used.
> +    Ranges are hyphen-separated intervals (such as `0-4`) and are inclusive
> +    on both sides. The numbers refer to pCPU ids.
> +
>  
>  Example
>  =======
> diff --git a/xen/arch/arm/dom0less-build.c b/xen/arch/arm/dom0less-build.c
> index 49d1f14d65..e364820189 100644
> --- a/xen/arch/arm/dom0less-build.c
> +++ b/xen/arch/arm/dom0less-build.c
> @@ -810,6 +810,68 @@ static int __init construct_domU(struct domain *d,
>      return rc;
>  }
>  
> +static void __init domain_vcpu_affinity(struct domain *d,
> +                                        const struct dt_device_node *node)
> +{
> +    const char *hard_affinity_str = NULL;
> +    struct dt_device_node *np;
> +    uint32_t val;
> +    int rc;
> +
> +    dt_for_each_child_node(node, np)
> +    {
> +        const char *s;
> +        struct vcpu *v;
> +        cpumask_t affinity;
> +
> +        if ( !dt_device_is_compatible(np, "xen,vcpu-affinity") )
> +            continue;
> +
> +        if ( !dt_property_read_u32(np, "id", &val) )
> +            continue;
> +
> +        if ( val >= d->max_vcpus )
> +            panic("Invalid vcpu_id %u for domain %s\n", val, dt_node_name(node));
> +
> +        v = d->vcpu[val];
> +        rc = dt_property_read_string(np, "hard-affinity", &hard_affinity_str);
> +        if ( rc < 0 )
> +            continue;
> +
> +        s = hard_affinity_str;
> +        cpumask_clear(&affinity);
> +        while ( *s != '\0' )
> +        {
> +            unsigned int start, end;
> +
> +            start = simple_strtoul(s, &s, 0);
> +
> +            if ( *s == '-' )    /* Range */
> +            {
> +                s++;
> +                end = simple_strtoul(s, &s, 0);
> +            }
> +            else                /* Single value */
> +                end = start;
> +
> +            if ( end >= nr_cpu_ids )
> +                panic("Invalid pCPU %u for domain %s\n", end, dt_node_name(node));
> +
> +            for ( ; start <= end; start++ )
> +                cpumask_set_cpu(start, &affinity);
> +
> +            if ( *s == ',' )
> +                s++;
> +            else if ( *s != '\0' )
> +                break;
> +        }
> +
> +        rc = vcpu_set_hard_affinity(v, &affinity);
> +        if ( rc )
> +            panic("vcpu%d: failed to set hard affinity\n", v->vcpu_id);
> +    }
> +}
> +
>  void __init create_domUs(void)
>  {
>      struct dt_device_node *node;
> @@ -992,6 +1054,8 @@ void __init create_domUs(void)
>          if ( rc )
>              panic("Could not set up domain %s (rc = %d)\n",
>                    dt_node_name(node), rc);
> +
> +        domain_vcpu_affinity(d, node);
>      }
>  }
>  
>
>