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

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Message-ID: <aEEbwQzSoVQAPqLq@yury>
Date: Thu, 5 Jun 2025 00:23:29 -0400
From: Yury Norov <yury.norov@...il.com>
To: "Jason A. Donenfeld" <Jason@...c4.com>,
	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 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;

I'll resend, sorry for noise.

>  
> -	if (unlikely(cpu >= nr_cpu_ids ||
> -		     !cpumask_test_cpu(cpu, cpu_online_mask))) {
> -		cpu_index = id % cpumask_weight(cpu_online_mask);
> -		cpu = cpumask_first(cpu_online_mask);
> -		for (i = 0; i < cpu_index; ++i)
> -			cpu = cpumask_next(cpu, cpu_online_mask);
> -		*stored_cpu = cpu;
> -	}
> -	return cpu;
> +	*stored_cpu = cpumask_nth(id % num_online_cpus(), cpu_online_mask);
> +	return *stored_cpu;
>  }
>  
>  /* This function is racy, in the sense that it's called while last_cpu is
> -- 
> 2.43.0