On Fri, Nov 1, 2024 at 11:12 AM mapicccy <guanjun@xxxxxxxxxxxxxxxxx> wrote:
>
>
>
> 2024年10月31日 18:50，Ming Lei <ming.lei@xxxxxxxxxx> 写道：
>
> On Thu, Oct 31, 2024 at 6:35 PM Thomas Gleixner <tglx@xxxxxxxxxxxxx> wrote:
>
>
> On Thu, Oct 31 2024 at 15:46, guanjun@xxxxxxxxxxxxxxxxx wrote:
>
> #ifdef CONFIG_SMP
>
> +static unsigned int __read_mostly managed_irqs_per_node;
> +static struct cpumask managed_irqs_cpumsk[MAX_NUMNODES] __cacheline_aligned_in_smp = {
> + [0 ... MAX_NUMNODES-1] = {CPU_BITS_ALL}
> +};
>
> +static void __group_prepare_affinity(struct cpumask *premask,
> + cpumask_var_t *node_to_cpumask)
> +{
> + nodemask_t nodemsk = NODE_MASK_NONE;
> + unsigned int ncpus, n;
> +
> + get_nodes_in_cpumask(node_to_cpumask, premask, &nodemsk);
> +
> + for_each_node_mask(n, nodemsk) {
> + cpumask_and(&managed_irqs_cpumsk[n], &managed_irqs_cpumsk[n], premask);
> + cpumask_and(&managed_irqs_cpumsk[n], &managed_irqs_cpumsk[n], node_to_cpumask[n]);
>
>
> How is this managed_irqs_cpumsk array protected against concurrency?
>
> + ncpus = cpumask_weight(&managed_irqs_cpumsk[n]);
> + if (ncpus < managed_irqs_per_node) {
> + /* Reset node n to current node cpumask */
> + cpumask_copy(&managed_irqs_cpumsk[n], node_to_cpumask[n]);
>
>
> This whole logic is incomprehensible and aside of the concurrency
> problem it's broken when CPUs are made present at run-time because these
> cpu masks are static and represent the stale state of the last
> invocation.
>
> Given the limitations of the x86 vector space, which is not going away
> anytime soon, there are only two options IMO to handle such a scenario.
>
> 1) Tell the nvme/block layer to disable queue affinity management
>
>
> +1
>
> There are other use cases, such as cpu isolation, which can benefit from
> this way too.
>
> https://lore.kernel.org/linux-nvme/20240702104112.4123810-1-ming.lei@xxxxxxxxxx/
>
I wonder if we need to do the same for virtio-blk.
>
> Thanks for your reminder. However, in this link only modified the NVMe driver,
> but there is the same issue in the virtio net driver as well.
I guess you meant virtio-blk actually?
>
> Guanjun
>
>
> Thanks,
>
Thanks
