netdev - Re: [PATCH 2/2 net-next] tcp: sk_add_backlog() is too agressive for TCP

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Date:	Tue, 24 Apr 2012 10:56:43 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Ilpo Järvinen <ilpo.jarvinen@...sinki.fi>
Cc:	David Miller <davem@...emloft.net>, rick.jones2@...com,
	Netdev <netdev@...r.kernel.org>, therbert@...gle.com,
	ncardwell@...gle.com, maze@...gle.com,
	Yuchung Cheng <ycheng@...gle.com>
Subject: Re: [PATCH 2/2 net-next] tcp: sk_add_backlog() is too agressive
 for TCP

On Tue, 2012-04-24 at 11:40 +0300, Ilpo Järvinen wrote:

> diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
> index 8bb6ade..33b87b2 100644
> --- a/net/ipv4/tcp.c
> +++ b/net/ipv4/tcp.c
> @@ -2820,7 +2820,11 @@ found:
>  	flush |= (__force int)(flags & TCP_FLAG_CWR);
>  	flush |= (__force int)((flags ^ tcp_flag_word(th2)) &
>  		  ~(TCP_FLAG_CWR | TCP_FLAG_FIN | TCP_FLAG_PSH));
> -	flush |= (__force int)(th->ack_seq ^ th2->ack_seq);
> +
> +	ackgap = skb_shinfo(p)->ack_size;
> +	ackdiff = th2->ack_seq - th->ack_seq;
> +	flush |= (ackdiff - 1) >= ackgap;
> +
>  	for (i = sizeof(*th); i < thlen; i += 4)
>  		flush |= *(u32 *)((u8 *)th + i) ^
>  			 *(u32 *)((u8 *)th2 + i);
> 

See how we duplicate tcp stack in GRO layer ;)

Really I have many doubts about GRO today.



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