netdev - Re: [PATCH v2 net-next] net: use jump_label to shortcut RPS if not setup

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Date:	Thu, 17 Nov 2011 22:34:49 +0100
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	David Miller <davem@...emloft.net>
Cc:	netdev <netdev@...r.kernel.org>, Tom Herbert <therbert@...gle.com>
Subject: Re: [PATCH v2 net-next] net: use jump_label to shortcut RPS if not
 setup

Le jeudi 17 novembre 2011 à 14:13 +0100, Eric Dumazet a écrit :
> Most machines dont use RPS/RFS, and pay a fair amount of instructions in
> netif_receive_skb() / netif_rx() / get_rps_cpu() just to discover
> RPS/RFS is not setup.
> 
> Add a jump_label named rps_needed.
> 
> If no device rps_map or global rps_sock_flow_table is setup,
> netif_receive_skb() / netif_rx() do a single instruction instead of many
> ones, including conditional jumps.
> 
> jmp +0    (if CONFIG_JUMP_LABEL=y)
> 
> Signed-off-by: Eric Dumazet <eric.dumazet@...il.com>
> CC: Tom Herbert <therbert@...gle.com>

I wonder if we could use this jump_label infrastructure to shortcut
expensive netfilter nf_hook_slow() / nf_iterate on empty
tables/chains...





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