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Message-ID: <490788B2.1060301@cosmosbay.com>
Date: Tue, 28 Oct 2008 22:48:34 +0100
From: Eric Dumazet <dada1@...mosbay.com>
To: Christian Bell <christian@...i.com>
CC: netdev@...r.kernel.org
Subject: Re: [PATCH 1/2] udp: introduce struct udp_table and multiple rwlocks
Christian Bell a écrit :
>
> 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.
Yes, I though about that. But : a full cache line is a waste of memory, and
choosing a power of two alignement is not easy because of 32bit/64bit arches,
and fact that sozepf(wrlock_t) can be > 4 if DEBUG
>
>> + } 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;
>> }
Good spoting, the write_unlock_bh(&hslot->lock); must be moved after the "fail:" label.
Thanks a lot
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