[Devel] Re: [PATCH net-2.6.25 1/3] Uninline the __inet_hash function

[Pavel Emelyanov]

Eric Dumazet wrote:
> Pavel Emelyanov a écrit :
>> Eric Dumazet wrote:
>>> Pavel Emelyanov a écrit :
>>>> This one is used in quite many places in the networking code and
>>>> seems to big to be inline.
>>>>
>>>> After the patch net/ipv4/build-in.o loses 725 bytes:
>>>> add/remove: 1/0 grow/shrink: 0/5 up/down: 374/-1099 (-725)
>>>> function                                     old     new   delta
>>>> __inet_hash                                    -     374    +374
>>>> tcp_sacktag_write_queue                     2255    2254      -1
>>>> __inet_lookup_listener                       284     274     -10
>>>> tcp_v4_syn_recv_sock                         755     495    -260
>>>> tcp_v4_hash                                  389      40    -349
>>>> inet_hash_connect                           1165     686    -479
>>>>
>>>> Exporting this is for dccp module.
>>>>
>>>> Signed-off-by: Pavel Emelyanov <xemul at openvz.org>
>>>>
>>>> ---
>>>>
>>>>  include/net/inet_hashtables.h |   27 ++-------------------------
>>>>  net/ipv4/inet_hashtables.c    |   27 +++++++++++++++++++++++++++
>>>>  2 files changed, 29 insertions(+), 25 deletions(-)
>>>>
>>>> diff --git a/include/net/inet_hashtables.h b/include/net/inet_hashtables.h
>>>> index 37f6cb1..1a43125 100644
>>>> --- a/include/net/inet_hashtables.h
>>>> +++ b/include/net/inet_hashtables.h
>>>> @@ -264,31 +264,8 @@ static inline void inet_listen_unlock(struct inet_hashinfo *hashinfo)
>>>>  		wake_up(&hashinfo->lhash_wait);
>>>>  }
>>>>  
>>>> -static inline void __inet_hash(struct inet_hashinfo *hashinfo,
>>>> -			       struct sock *sk, const int listen_possible)
>>>> -{
>>>> -	struct hlist_head *list;
>>>> -	rwlock_t *lock;
>>>> -
>>>> -	BUG_TRAP(sk_unhashed(sk));
>>>> -	if (listen_possible && sk->sk_state == TCP_LISTEN) {
>>>> -		list = &hashinfo->listening_hash[inet_sk_listen_hashfn(sk)];
>>>> -		lock = &hashinfo->lhash_lock;
>>>> -		inet_listen_wlock(hashinfo);
>>>> -	} else {
>>>> -		struct inet_ehash_bucket *head;
>>>> -		sk->sk_hash = inet_sk_ehashfn(sk);
>>>> -		head = inet_ehash_bucket(hashinfo, sk->sk_hash);
>>>> -		list = &head->chain;
>>>> -		lock = inet_ehash_lockp(hashinfo, sk->sk_hash);
>>>> -		write_lock(lock);
>>>> -	}
>>>> -	__sk_add_node(sk, list);
>>>> -	sock_prot_inc_use(sk->sk_prot);
>>>> -	write_unlock(lock);
>>>> -	if (listen_possible && sk->sk_state == TCP_LISTEN)
>>>> -		wake_up(&hashinfo->lhash_wait);
>>>> -}
>>>> +extern void __inet_hash(struct inet_hashinfo *hashinfo, struct sock *sk,
>>>> +		const int listen_possible);
>>>>  
>>>>  static inline void inet_hash(struct inet_hashinfo *hashinfo, struct sock *sk)
>>>>  {
>>>> diff --git a/net/ipv4/inet_hashtables.c b/net/ipv4/inet_hashtables.c
>>>> index 67704da..46f899b 100644
>>>> --- a/net/ipv4/inet_hashtables.c
>>>> +++ b/net/ipv4/inet_hashtables.c
>>>> @@ -267,6 +267,33 @@ static inline u32 inet_sk_port_offset(const struct sock *sk)
>>>>  					  inet->dport);
>>>>  }
>>>>  
>>>> +void __inet_hash(struct inet_hashinfo *hashinfo, struct sock *sk,
>>>> +		const int listen_possible)
>>>> +{
>>>> +	struct hlist_head *list;
>>>> +	rwlock_t *lock;
>>>> +
>>>> +	BUG_TRAP(sk_unhashed(sk));
>>>> +	if (listen_possible && sk->sk_state == TCP_LISTEN) {
>>>> +		list = &hashinfo->listening_hash[inet_sk_listen_hashfn(sk)];
>>>> +		lock = &hashinfo->lhash_lock;
>>>> +		inet_listen_wlock(hashinfo);
>>>> +	} else {
>>>> +		struct inet_ehash_bucket *head;
>>>> +		sk->sk_hash = inet_sk_ehashfn(sk);
>>>> +		head = inet_ehash_bucket(hashinfo, sk->sk_hash);
>>>> +		list = &head->chain;
>>>> +		lock = inet_ehash_lockp(hashinfo, sk->sk_hash);
>>>> +		write_lock(lock);
>>>> +	}
>>>> +	__sk_add_node(sk, list);
>>>> +	sock_prot_inc_use(sk->sk_prot);
>>>> +	write_unlock(lock);
>>>> +	if (listen_possible && sk->sk_state == TCP_LISTEN)
>>>> +		wake_up(&hashinfo->lhash_wait);
>>>> +}
>>>> +EXPORT_SYMBOL_GPL(__inet_hash);
>>>> +
>>>>  /*
>>>>   * Bind a port for a connect operation and hash it.
>>>>   */
>>> If you un-inline this (good idea), I am not sure we still need listen_possible 
>>> argument.
>>>
>>> It was usefull only to help compiler to zap dead code (since it was known at 
>>> compile time), now it only adds some extra test and argument passing.
>> Hm... I've tried to address this issue and got worse result - minus
>> 600 bytes (vs minus 725). So, what would be more preferable - get a 
>> smaller code with one extra 'if' or get a bit larger code without it?
>>
> 
> Strange... What I meant is always assume listen_possible is true.

That's not truth, if I get you right. The __inet_hash() is called
with 0, from all the places except for the inet_hash() one.

> The if (sk->sk_state == TCP_LISTEN) will finally see the truth.
> 
> I did a test here on x86 gcc-4.2.2 and saved 32 bytes.
> 
> 
> 

Thanks,
Pavel