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

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Message-ID: <t2t412e6f7f1004220527mb5340bebye1d1fda0963dcf2a@mail.gmail.com>
Date:	Thu, 22 Apr 2010 20:27:16 +0800
From:	Changli Gao <xiaosuo@...il.com>
To:	David Miller <davem@...emloft.net>,
	Eric Dumazet <eric.dumazet@...il.com>
Cc:	hadi@...erus.ca, therbert@...gle.com, netdev@...r.kernel.org
Subject: Re: [PATCH v5] net: batch skb dequeueing from softnet input_pkt_queue

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?
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