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

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Date:	Wed, 01 Jun 2011 14:13:19 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Frank Blaschka <blaschka@...ux.vnet.ibm.com>
Cc:	davem@...emloft.net, netdev@...r.kernel.org,
	linux-s390@...r.kernel.org, heiko.carstens@...ibm.com
Subject: Re: [BUG] net: cpu offline cause napi stall

Le mercredi 01 juin 2011 à 12:33 +0200, Frank Blaschka a écrit :
> Hi Dave, Eric,
> 
> 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. Do you think this could cause the stall or
> did I miss something?
> 
> Thx for your help.

Hi Frank

I believe you are right, I cant see where the poll_list transfert from
dead cpu to online cpu is done.

Do you want to prepare a patch ?

Thanks !



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