[PATCH 6/6] [TCP]: Reorganize struct tcp_sock to save 16 bytes on 64-bit arch

[PATCH 6/6] [TCP]: Reorganize struct tcp_sock to save 16 bytes on 64-bit arch

[Arnaldo Carvalho de Melo]

/home/acme/git/net-2.6/net/ipv6/tcp_ipv6.c:
  struct tcp_sock  |  -16
  struct tcp6_sock |  -16
 2 structs changed

Now it is at:

/* size: 1552, cachelines: 25 */
/* paddings: 2, sum paddings: 8 */
/* last cacheline: 16 bytes */

As soon as we stop using skb_queue_list we'll get it down to 24 cachelines.

Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
---
 include/linux/tcp.h |    6 ++++--
 1 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/include/linux/tcp.h b/include/linux/tcp.h
index 08027f1..f48644d 100644
--- a/include/linux/tcp.h
+++ b/include/linux/tcp.h
@@ -304,7 +304,6 @@ struct tcp_sock {
 	u32	rtt_seq;	/* sequence number to update rttvar	*/
 
 	u32	packets_out;	/* Packets which are "in flight"	*/
-	u32	retrans_out;	/* Retransmitted packets out		*/
 /*
  *      Options received (usually on last packet, some only on SYN packets).
  */
@@ -332,6 +331,8 @@ struct tcp_sock {
 
 	struct tcp_sack_block recv_sack_cache[4];
 
+	u32	retrans_out;	/* Retransmitted packets out		*/
+
 	struct sk_buff *highest_sack;   /* highest skb with SACK received
 					 * (validity guaranteed only if
 					 * sacked_out > 0)
@@ -372,7 +373,6 @@ struct tcp_sock {
 
 	unsigned int		keepalive_time;	  /* time before keep alive takes place */
 	unsigned int		keepalive_intvl;  /* time interval between keep alive probes */
-	int			linger2;
 
 	unsigned long last_synq_overflow; 
 
@@ -398,6 +398,8 @@ struct tcp_sock {
 		u32		  probe_seq_end;
 	} mtu_probe;
 
+	int			linger2;
+
 #ifdef CONFIG_TCP_MD5SIG
 /* TCP AF-Specific parts; only used by MD5 Signature support so far */
 	struct tcp_sock_af_ops	*af_specific;
-- 
1.5.3.8

Re: [PATCH 6/6] [TCP]: Reorganize struct tcp_sock to save 16 bytes

[Eric Dumazet]

Arnaldo Carvalho de Melo a écrit :
> /home/acme/git/net-2.6/net/ipv6/tcp_ipv6.c:
>   struct tcp_sock  |  -16
>   struct tcp6_sock |  -16
>  2 structs changed
> 
> Now it is at:
> 
> /* size: 1552, cachelines: 25 */
> /* paddings: 2, sum paddings: 8 */
> /* last cacheline: 16 bytes */
> 
> As soon as we stop using skb_queue_list we'll get it down to 24 cachelines.
> 
> Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
> ---
>  include/linux/tcp.h |    6 ++++--
>  1 files changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/include/linux/tcp.h b/include/linux/tcp.h
> index 08027f1..f48644d 100644
> --- a/include/linux/tcp.h
> +++ b/include/linux/tcp.h
> @@ -304,7 +304,6 @@ struct tcp_sock {
>  	u32	rtt_seq;	/* sequence number to update rttvar	*/
>  
>  	u32	packets_out;	/* Packets which are "in flight"	*/
> -	u32	retrans_out;	/* Retransmitted packets out		*/
>  /*
>   *      Options received (usually on last packet, some only on SYN packets).
>   */
> @@ -332,6 +331,8 @@ struct tcp_sock {
>  
>  	struct tcp_sack_block recv_sack_cache[4];
>  
> +	u32	retrans_out;	/* Retransmitted packets out		*/
> +

Hum... retrans_out should sit close to packets_out (or lost_out/sacked_out 
???), please.

'struct tcp_sock' is very large on 64 bits, so I would prefer to make sure 
most paths dont need to touch all 24 cache lines (or 25 cache lines).

Re: [PATCH 6/6] [TCP]: Reorganize struct tcp_sock to save 16 bytes

[Arnaldo Carvalho de Melo]

Em Thu, Jan 31, 2008 at 08:57:53PM +0100, Eric Dumazet escreveu:
> Arnaldo Carvalho de Melo a écrit :
>> /home/acme/git/net-2.6/net/ipv6/tcp_ipv6.c:
>>   struct tcp_sock  |  -16
>>   struct tcp6_sock |  -16
>>  2 structs changed
>>
>> Now it is at:
>>
>> /* size: 1552, cachelines: 25 */
>> /* paddings: 2, sum paddings: 8 */
>> /* last cacheline: 16 bytes */
>>
>> As soon as we stop using skb_queue_list we'll get it down to 24 cachelines.
>>
>> Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
>> ---
>>  include/linux/tcp.h |    6 ++++--
>>  1 files changed, 4 insertions(+), 2 deletions(-)
>>
>> diff --git a/include/linux/tcp.h b/include/linux/tcp.h
>> index 08027f1..f48644d 100644
>> --- a/include/linux/tcp.h
>> +++ b/include/linux/tcp.h
>> @@ -304,7 +304,6 @@ struct tcp_sock {
>>  	u32	rtt_seq;	/* sequence number to update rttvar	*/
>>   	u32	packets_out;	/* Packets which are "in flight"	*/
>> -	u32	retrans_out;	/* Retransmitted packets out		*/
>>  /*
>>   *      Options received (usually on last packet, some only on SYN packets).
>>   */
>> @@ -332,6 +331,8 @@ struct tcp_sock {
>>   	struct tcp_sack_block recv_sack_cache[4];
>>  +	u32	retrans_out;	/* Retransmitted packets out		*/
>> +
>
> Hum... retrans_out should sit close to packets_out (or lost_out/sacked_out 
> ???), please.
>
> 'struct tcp_sock' is very large on 64 bits, so I would prefer to make sure 
> most paths dont need to touch all 24 cache lines (or 25 cache lines).

That is perfectly fine, I'll replace my patch with another, that states
this beyond doubt.

- Arnaldo

Re: [PATCH 6/6] [TCP]: Reorganize struct tcp_sock to save 16 bytes

[Arnaldo Carvalho de Melo]

Em Thu, Jan 31, 2008 at 06:17:20PM -0200, Arnaldo Carvalho de Melo escreveu:
> Em Thu, Jan 31, 2008 at 08:57:53PM +0100, Eric Dumazet escreveu:
> > Hum... retrans_out should sit close to packets_out (or lost_out/sacked_out 
> > ???), please.
> >
> > 'struct tcp_sock' is very large on 64 bits, so I would prefer to make sure 
> > most paths dont need to touch all 24 cache lines (or 25 cache lines).
> 
> That is perfectly fine, I'll replace my patch with another, that states
> this beyond doubt.

David, I just removed this patch from my net-2.6 tree, if you are ok
with the others, please pull.

- Arnaldo