netdev - Re: [RFC net-next 3/6] gve: Use napi_affinity_no

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Message-ID: <ZrvTzX8CfyM40c8I@LQ3V64L9R2.home>
Date: Tue, 13 Aug 2024 22:44:45 +0100
From: Joe Damato <jdamato@...tly.com>
To: Shailend Chand <shailend@...gle.com>
Cc: netdev@...r.kernel.org, Jeroen de Borst <jeroendb@...gle.com>,
	Praveen Kaligineedi <pkaligineedi@...gle.com>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Willem de Bruijn <willemb@...gle.com>,
	Harshitha Ramamurthy <hramamurthy@...gle.com>,
	Ziwei Xiao <ziweixiao@...gle.com>,
	open list <linux-kernel@...r.kernel.org>
Subject: Re: [RFC net-next 3/6] gve: Use napi_affinity_no_change

On Tue, Aug 13, 2024 at 11:55:31AM -0700, Shailend Chand wrote:
> On Mon, Aug 12, 2024 at 7:57 AM Joe Damato <jdamato@...tly.com> wrote:
> >
> > Use napi_affinity_no_change instead of gve's internal implementation,
> > simplifying and centralizing the logic.
> >
> > Signed-off-by: Joe Damato <jdamato@...tly.com>
> > ---
> >  drivers/net/ethernet/google/gve/gve_main.c | 14 +-------------
> >  1 file changed, 1 insertion(+), 13 deletions(-)
> >
> > diff --git a/drivers/net/ethernet/google/gve/gve_main.c b/drivers/net/ethernet/google/gve/gve_main.c
> > index 661566db68c8..ad5e85b8c6a5 100644
> > --- a/drivers/net/ethernet/google/gve/gve_main.c
> > +++ b/drivers/net/ethernet/google/gve/gve_main.c
> > @@ -298,18 +298,6 @@ static irqreturn_t gve_intr_dqo(int irq, void *arg)
> >         return IRQ_HANDLED;
> >  }
> >
> > -static int gve_is_napi_on_home_cpu(struct gve_priv *priv, u32 irq)
> > -{
> > -       int cpu_curr = smp_processor_id();
> > -       const struct cpumask *aff_mask;
> > -
> > -       aff_mask = irq_get_effective_affinity_mask(irq);
> > -       if (unlikely(!aff_mask))
> > -               return 1;
> > -
> > -       return cpumask_test_cpu(cpu_curr, aff_mask);
> > -}
> > -
> >  int gve_napi_poll(struct napi_struct *napi, int budget)
> >  {
> >         struct gve_notify_block *block;
> > @@ -383,7 +371,7 @@ int gve_napi_poll_dqo(struct napi_struct *napi, int budget)
> >                 /* Reschedule by returning budget only if already on the correct
> >                  * cpu.
> >                  */
> > -               if (likely(gve_is_napi_on_home_cpu(priv, block->irq)))
> > +               if (likely(napi_affinity_no_change(block->irq)))
> 
> Nice to centralize this code! Evolving this to cache the affinity mask
> like the other drivers would probably also require a means to update
> the cache when the affinity changes.

Thanks for taking a look.

The gve driver already calls irq_get_effective_affinity_mask in the
hot path, so I'm planning on submitting a rfcv2 which will do this:

-               if (likely(gve_is_napi_on_home_cpu(priv, block->irq)))
+               const struct cpumask *aff_mask =
+                       irq_get_effective_affinity_mask(block->irq);
+
+               if (likely(napi_affinity_no_change(aff_mask)))
                        return budget;

with a change like that there'd be no behavioral change to gve since
it didn't cache before and still won't be caching after this change.

I think a change can be made to gve in a separate patch set to
support caching the affinity mask and does not need to be included
with this change.

What do you think?