netdev - Re: [PATCH] net: cpu offline cause napi stall

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Message-Id: <20110607.010136.1857896380762569754.davem@davemloft.net>
Date:	Tue, 07 Jun 2011 01:01:36 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	eric.dumazet@...il.com
Cc:	heiko.carstens@...ibm.com, blaschka@...ux.vnet.ibm.com,
	netdev@...r.kernel.org, linux-s390@...r.kernel.org
Subject: Re: [PATCH] net: cpu offline cause napi stall

From: Eric Dumazet <eric.dumazet@...il.com>
Date: Tue, 07 Jun 2011 08:50:03 +0200

> From: Heiko Carstens <heiko.carstens@...ibm.com>
> 
> Frank Blaschka reported :
> <quote>
>   During heavy network load we turn off/on cpus.
>   Sometimes this causes a stall on the network device.
>   Digging into the dump I found out following:
> 
>   napi is scheduled but does not run. From the I/O buffers
>   and the napi state I see napi/rx_softirq processing has stopped
>   because the budget was reached. napi stays in the
>   softnet_data poll_list and the rx_softirq was raised again.
> 
>   I assume at this time the cpu offline comes in,
>   the rx softirq is raised/moved to another cpu but napi stays in the
>   poll_list of the softnet_data of the now offline cpu.
> 
>   Reviewing dev_cpu_callback (net/core/dev.c) I did not find the
>   poll_list is transfered to the new cpu.
> </quote>
> 
> This patch is a straightforward implementation of Frank suggestion :
> 
> Transfert poll_list and trigger NET_RX_SOFTIRQ on new cpu.
> 
> Reported-by: Frank Blaschka <blaschka@...ux.vnet.ibm.com>
> Signed-off-by: Heiko Carstens <heiko.carstens@...ibm.com>
> Signed-off-by: Eric Dumazet <eric.dumazet@...il.com>
> Tested-by: Eric Dumazet <eric.dumazet@...il.com>

Applied, thanks everyone.
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