netdev - Re: [PATCH net-next 2/6] ipv6: fib6_new

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Date:   Wed, 16 Nov 2022 17:05:46 -0700
From:   David Ahern <dsahern@...nel.org>
To:     Eric Dumazet <edumazet@...gle.com>,
        "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>
Cc:     netdev@...r.kernel.org, eric.dumazet@...il.com
Subject: Re: [PATCH net-next 2/6] ipv6: fib6_new_sernum() optimization

On 11/15/22 2:10 AM, Eric Dumazet wrote:
> Adopt atomic_try_cmpxchg() which is slightly more efficient.
> 
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> Cc: David Ahern <dsahern@...nel.org>
> ---
>  net/ipv6/ip6_fib.c | 7 +++----
>  1 file changed, 3 insertions(+), 4 deletions(-)
> 
> diff --git a/net/ipv6/ip6_fib.c b/net/ipv6/ip6_fib.c
> index 413f66781e50de62d6b20042d84798e7da59165a..2438da5ff6da810d9f612fc66df4d28510f50f10 100644
> --- a/net/ipv6/ip6_fib.c
> +++ b/net/ipv6/ip6_fib.c
> @@ -91,13 +91,12 @@ static void fib6_walker_unlink(struct net *net, struct fib6_walker *w)
>  
>  static int fib6_new_sernum(struct net *net)
>  {
> -	int new, old;
> +	int new, old = atomic_read(&net->ipv6.fib6_sernum);
>  
>  	do {
> -		old = atomic_read(&net->ipv6.fib6_sernum);
>  		new = old < INT_MAX ? old + 1 : 1;
> -	} while (atomic_cmpxchg(&net->ipv6.fib6_sernum,
> -				old, new) != old);
> +	} while (!atomic_try_cmpxchg(&net->ipv6.fib6_sernum, &old, new));
> +
>  	return new;
>  }
>  

Reviewed-by: David Ahern <dsahern@...nel.org>