netdev - Re: [RFC] [PATCH 1/5] net: Introduce sk_tx_queue

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Message-ID: <4AD6FA27.1040804@gmail.com>
Date:	Thu, 15 Oct 2009 12:32:07 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Krishna Kumar <krkumar2@...ibm.com>
CC:	davem@...emloft.net, netdev@...r.kernel.org,
	herbert@...dor.apana.org.au
Subject: Re: [RFC] [PATCH 1/5] net: Introduce sk_tx_queue_mapping

Krishna Kumar a écrit :
> From: Krishna Kumar <krkumar2@...ibm.com>
> 
> Introduce sk_tx_queue_mapping; and functions that set, test and get
> this value. Reset sk_tx_queue_mapping to -1 whenever the dst cache
> is set/reset, and in socket alloc & free (free probably doesn't need
> it).
> 
> Signed-off-by: Krishna Kumar <krkumar2@...ibm.com>
> ---
>  include/net/sock.h |   21 +++++++++++++++++++++
>  net/core/sock.c    |    7 ++++++-
>  2 files changed, 27 insertions(+), 1 deletion(-)
> 
> diff -ruNp org/include/net/sock.h new/include/net/sock.h
> --- org/include/net/sock.h	2009-10-14 10:36:52.000000000 +0530
> +++ new/include/net/sock.h	2009-10-14 17:59:44.000000000 +0530
> @@ -107,6 +107,7 @@ struct net;
>   *	@skc_node: main hash linkage for various protocol lookup tables
>   *	@skc_nulls_node: main hash linkage for UDP/UDP-Lite protocol
>   *	@skc_refcnt: reference count
> + *	@skc_tx_queue_mapping: tx queue number for this connection
>   *	@skc_hash: hash value used with various protocol lookup tables
>   *	@skc_family: network address family
>   *	@skc_state: Connection state
> @@ -128,6 +129,7 @@ struct sock_common {
>  		struct hlist_nulls_node skc_nulls_node;
>  	};
>  	atomic_t		skc_refcnt;
> +	int			skc_tx_queue_mapping;
>  

Hmm, two remarks :

1) It adds a 32bits hole on 64bit arches
2) sk_tx_queue_mapping is only read in tx path, but sits close to
skc_refcnt, which is now only read/written in rx path (by socket lookups)

But since sock_common is small, 56 bytes on x86_64,(under a cache line),
there is nothing we can do at this moment.

My plan is to move skc_refcnt at the end of sock_common and I'll need to add
new generic fields into sock_common to make offsetof(skc_refcnt) = 64.

Next to sock_common, will be placed fields used in rx path.

Acked-by: Eric Dumazet <eric.dumazet@...il.com>
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