netdev - Re: [PATCH] net: fix softnet

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Message-ID: <p2t412e6f7f1004142122w115b2855o3880467da5cc1e2d@mail.gmail.com>
Date:	Thu, 15 Apr 2010 12:22:51 +0800
From:	Changli Gao <xiaosuo@...il.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	"David S. Miller" <davem@...emloft.net>,
	Tom Herbert <therbert@...gle.com>, netdev@...r.kernel.org
Subject: Re: [PATCH] net: fix softnet_stat

On Thu, Apr 15, 2010 at 12:14 PM, Eric Dumazet <eric.dumazet@...il.com> wrote:
> Le jeudi 15 avril 2010 à 05:40 +0200, Eric Dumazet a écrit :
>
> Oh well, I revert this comment, we need a mutual exclusion between cpus
> if we dont want to miss some increments, even in a slow path.
>
> __get_cpu_var(netdev_rx_stat).field++; is safe because updated only by
> this cpu.
>
> Once you use per_cpu(netdev_rx_stat, cpu).field++; you need a
> synchronization since this is not atomic.
>

rps_unlock() is a synchronization if needed.

> so queue->dropped++ is safer and faster too (inside the rps_lock
> section)
>

It involves more lines of code, moving netdev_rx_stat into softdata.

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