netdev - Re: [PATCH v4] net: batch skb dequeueing from softnet input_pkt

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Date:	Thu, 22 Apr 2010 16:03:21 +0800
From:	Changli Gao <xiaosuo@...il.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Stephen Hemminger <shemminger@...tta.com>,
	"David S. Miller" <davem@...emloft.net>, jamal <hadi@...erus.ca>,
	Tom Herbert <therbert@...gle.com>, netdev@...r.kernel.org
Subject: Re: [PATCH v4] net: batch skb dequeueing from softnet input_pkt_queue

On Thu, Apr 22, 2010 at 3:21 PM, Eric Dumazet <eric.dumazet@...il.com> wrote:
> Jamal perf reports show lock contention but also cache line ping pongs.
>
> Yet, you keep a process_queue_len shared by producers and consumer.
>
> Producers want to read it, while consumer decrement it (dirtying its
> cache line) every packet, slowing down the things.
>
>
> The idea of batching is to let the consumer process its local queue with
> no impact to producers.
>
> Please remove it completely, or make the consumer zero it only at the
> end of batch processing.
>
> A cache line miss cost is about 120 cycles. Multiply it by 1 million
> packet per second...
>

OK, I'll remove it, and update the input_pkt_queue only before
process_backlog returns.


-- 
Regards，
Changli Gao(xiaosuo@...il.com)
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