netdev - Re: [PATCH 1/2] udp: introduce struct udp

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Message-Id: <B7C6414D-7A69-48DA-8424-5D9F5FC50338@myri.com>
Date:	Tue, 28 Oct 2008 14:23:55 -0700
From:	Christian Bell <christian@...i.com>
To:	Eric Dumazet <dada1@...mosbay.com>
Cc:	netdev@...r.kernel.org
Subject: Re: [PATCH 1/2] udp: introduce struct udp_table and multiple rwlocks


On Oct 28, 2008, at 1:37 PM, Eric Dumazet wrote:

> -extern struct hlist_head udp_hash[UDP_HTABLE_SIZE];
> -extern rwlock_t udp_hash_lock;
> +struct udp_hslot {
> +	struct hlist_head	head;
> +	rwlock_t		lock;
> +};

This structure should be aligned up to cacheline to reduce false  
sharing of more than one hslot.

> +	} else {
> +		hslot = &udptable->hash[udp_hashfn(net, snum)];
> +		write_lock_bh(&hslot->lock);
> +		if (udp_lib_lport_inuse(net, snum, hslot, sk, saddr_comp))
> +			goto fail;

The fail: label below should still unlock_bh when the above condition  
fails.

>
> +	}
> 	inet_sk(sk)->num = snum;
> 	sk->sk_hash = snum;
> 	if (sk_unhashed(sk)) {
> -		sk_add_node(sk, &udptable[udp_hashfn(net, snum)]);
> +		sk_add_node(sk, &hslot->head);
> 		sock_prot_inuse_add(sock_net(sk), sk->sk_prot, 1);
> 	}
> +	write_unlock_bh(&hslot->lock);
> 	error = 0;
> fail:
> -	write_unlock_bh(&udp_hash_lock);
> 	return error;
> }

cheers,

	. . christian
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