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

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Message-ID: <CANLc=auVkEWwhEHVwK9UkdjJJ5z9FTRS6wK=zb9pCgoAm4CWdw@mail.gmail.com>
Date: Tue, 13 Aug 2024 14:50:05 -0700
From: Shailend Chand <shailend@...gle.com>
To: Joe Damato <jdamato@...tly.com>, Shailend Chand <shailend@...gle.com>, 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 2:44 PM Joe Damato <jdamato@...tly.com> wrote:
>
> 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?

Sounds good!