Re: [Intel-wired-lan] [PATCH net-next v2 4/8] net: napi: add CPU affinity to napi->config

[Ahmed Zaki]

On 2024-12-20 10:23 a.m., Jakub Kicinski wrote:
On Fri, 20 Dec 2024 07:51:09 -0700 Ahmed Zaki wrote:
On 2024-12-19 8:42 p.m., Jakub Kicinski wrote:
On Wed, 18 Dec 2024 09:58:39 -0700 Ahmed Zaki wrote:
+       if (!glue_created && flags & NAPIF_IRQ_AFFINITY) {
+               glue = kzalloc(sizeof(*glue), GFP_KERNEL);
+               if (!glue)
+                       return;
+               glue->notify.notify = netif_irq_cpu_rmap_notify;
+               glue->notify.release = netif_napi_affinity_release;
+               glue->data = napi;
+               glue->rmap = NULL;
+               napi->irq_flags |= NAPIF_IRQ_NORMAP;

Why allocate the glue? is it not possible to add the fields:

        struct irq_affinity_notify notify;
        u16 index;

to struct napi_struct ?

In the first branch of "if", the cb function netif_irq_cpu_rmap_notify()
is also passed to irq_cpu_rmap_add() where the irq notifier is embedded
in "struct irq_glue".

I don't understand what you're trying to say, could you rephrase?

Sure. After this patch, we have (simplified):

void netif_napi_set_irq(struct napi_struct *napi, int irq, unsigned long 
flags)
 {
        struct irq_glue *glue = NULL;
        int  rc;

        napi->irq = irq;

 #ifdef CONFIG_RFS_ACCEL
        if (napi->dev->rx_cpu_rmap && flags & NAPIF_IRQ_ARFS_RMAP) {
                rc = irq_cpu_rmap_add(napi->dev->rx_cpu_rmap, irq, napi,
                                      netif_irq_cpu_rmap_notify);
                .
                .
                .
        }
 #endif

        if (flags & NAPIF_IRQ_AFFINITY) {
                glue = kzalloc(sizeof(*glue), GFP_KERNEL);
                if (!glue)
                        return;
                glue->notify.notify = netif_irq_cpu_rmap_notify;
                glue->notify.release = netif_napi_affinity_release;
                .
                .
        }
 }


Both branches assign the new cb function "netif_irq_cpu_rmap_notify()" 
as the new IRQ notifier, but the first branch calls irq_cpu_rmap_add() 
where the notifier is embedded in "struct irq_glue". So the cb function 
needs to assume the notifier is inside irq_glue, so the second "if" 
branch needs to do the same.



I think this cannot be changed as long as some drivers are directly
calling irq_cpu_rmap_add() instead of the proposed API.

Drivers which are not converted shouldn't matter if we have our own
notifier and call cpu_rmap_update() directly, no?


Only dependency is that irq_cpu_rmap_add() puts notifier inside irq_glue.

Drivers which are converted should not call irq_cpu_rmap_add().

Correct, they don't.