Re: [PATCH 2/2] x86/numa: introduce per-NUMA node flush locks

[Jan Beulich <jbeulich@xxxxxxxx>]

On 22.05.2025 10:48, Roger Pau Monne wrote:
> +bool flush_numa_node(const cpumask_t *mask, const void *va, unsigned int 
> flags)
> +{
> +    nodeid_t node = num_online_nodes() > 1 ? cpumask_to_node(mask)
> +                                           : NUMA_NO_NODE;
> +    struct arch_numa_node *info;
> +
> +    if ( node == NUMA_NO_NODE )
> +        return false;

One further question: Here you limit NUMA flushing to a single node, using
global flushes in all other cases. Did you consider extending this? Savings
ought to be had also when you want to e.g. flush on 2 out of 8 nodes. That
is, would it perhaps make sense to break up the file-scope flush_* variables
in smp.c altogether, using the NUMA approach uniformly?

> +    info = node_info[node];

node_info[0] would then need populating from a static struct instance, of
course, and ...

> +    if ( !info )
> +        return false;

... such conditionals of course would need to go away. Then we'd also get
away without requiring yet another direct-APIC-vector, as ...

> +    spin_lock(&info->flush_lock);
> +    cpumask_and(&info->flush_mask, mask, &cpu_online_map);
> +    cpumask_clear_cpu(smp_processor_id(), &info->flush_mask);
> +    info->flush_va = va;
> +    info->flush_flags = flags;
> +    send_IPI_mask(&info->flush_mask, INVALIDATE_NUMA_VECTOR);

... INVALIDATE_TLB_VECTOR could then be used here.

Jan

> +    while ( !cpumask_empty(&info->flush_mask) )
> +        cpu_relax();
> +    spin_unlock(&info->flush_lock);
> +
> +    return true;
> +}