netdev - Re: [PATCH] wireguard/queueing: simplify wg_cpumask_next

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Message-ID: <aEGAfy80UcB_UMYs@zx2c4.com>
Date: Thu, 5 Jun 2025 13:33:19 +0200
From: "Jason A. Donenfeld" <Jason@...c4.com>
To: Yury Norov <yury.norov@...il.com>
Cc: Andrew Lunn <andrew+netdev@...n.ch>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	wireguard@...ts.zx2c4.com, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] wireguard/queueing: simplify wg_cpumask_next_online()

On Thu, Jun 05, 2025 at 12:23:29AM -0400, Yury Norov wrote:
> On Wed, Jun 04, 2025 at 07:36:55PM -0400, Yury Norov wrote:
> > wg_cpumask_choose_online() opencodes cpumask_nth(). Use it and make the
> > function significantly simpler. While there, fix opencoded cpu_online()
> > too. 
> > 
> > Signed-off-by: Yury Norov <yury.norov@...il.com>
> > ---
> >  drivers/net/wireguard/queueing.h | 14 ++++----------
> >  1 file changed, 4 insertions(+), 10 deletions(-)
> > 
> > diff --git a/drivers/net/wireguard/queueing.h b/drivers/net/wireguard/queueing.h
> > index 7eb76724b3ed..3bfe16f71af0 100644
> > --- a/drivers/net/wireguard/queueing.h
> > +++ b/drivers/net/wireguard/queueing.h
> > @@ -104,17 +104,11 @@ static inline void wg_reset_packet(struct sk_buff *skb, bool encapsulating)
> >  
> >  static inline int wg_cpumask_choose_online(int *stored_cpu, unsigned int id)
> >  {
> > -	unsigned int cpu = *stored_cpu, cpu_index, i;
> > +	if (likely(*stored_cpu < nr_cpu_ids && cpu_online(*stored_cpu)))
> > +		return cpu;
> 
> Oops... This should be 
>                 return *stored_cpu;

Maybe it's best to structure the function something like:

unsigned int cpu = *stored_cpu;
if (unlikely(cpu >= nr_cpu_ids || !cpu_online(cpu))) {
	cpu = *stored_cpu = cpumask_nth(id % num_online_cpus(),	cpu_online_mask);
return cpu;