netdev - Re: [PATCH v5] net: batch skb dequeueing from softnet input_pkt

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Date:	Thu, 22 Apr 2010 16:24:31 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Changli Gao <xiaosuo@...il.com>
Cc:	David Miller <davem@...emloft.net>, hadi@...erus.ca,
	therbert@...gle.com, netdev@...r.kernel.org
Subject: Re: [PATCH v5] net: batch skb dequeueing from softnet
 input_pkt_queue

Le jeudi 22 avril 2010 à 20:27 +0800, Changli Gao a écrit :
> On Thu, Apr 22, 2010 at 5:43 PM, David Miller <davem@...emloft.net> wrote:
> > From: Changli Gao <xiaosuo@...il.com>
> > Date: Thu, 22 Apr 2010 17:09:17 +0800
> >
> >> +     unsigned int            input_pkt_queue_len;
> >> +     struct sk_buff          *input_pkt_queue_head;
> >> +     struct sk_buff          **input_pkt_queue_tailp;
> >> +
> >
> > Please do not ignore Stephen Hemminger's feedback.
> >
> > We already have enough odd SKB queue implementations, we
> > do not need yet another one in a core location.  This makes
> > it harder and harder to eventually convert sk_buff to use
> > "struct list_head".
> >
> > Instead, use "struct sk_buff_head" and the lockless accessors
> > (__skb_insert, etc.) and initializer (__skb_queue_head_init).
> >
> 
> If I want to keep softnet_data small, I have to access the internal
> fields of sk_buff_head, and modify them in a hack way. It doesn't
> sound good. If not, softnet_data will become:
> 
> struct softnet_data {
>         struct Qdisc            *output_queue;
>         struct list_head        poll_list;
>         struct sk_buff          *completion_queue;
>         struct sk_buff_head     process_queue;
> 
> #ifdef CONFIG_RPS
>         struct softnet_data     *rps_ipi_list;
> 
>         /* Elements below can be accessed between CPUs for RPS */
>         struct call_single_data csd ____cacheline_aligned_in_smp;
>         struct softnet_data     *rps_ipi_next;
>         unsigned int            cpu;
>         unsigned int            input_queue_head;
> #endif
>         unsigned int            input_pkt_queue_len;
>         struct sk_buff_head     input_pkt_queue;
>         struct napi_struct      backlog;
> };
> 
> Eric, do you think it is too fat?

No it is not, as long as we are careful to separate cache lines.

By the way, input_pkt_queue_len is already in input_ptk_queue (.len)

Thanks


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