netdev - Re: NOHZ: local_softirq

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Message-ID: <4ADF5710.4030505@imap.cc>
Date:	Wed, 21 Oct 2009 20:46:40 +0200
From:	Tilman Schmidt <tilman@...p.cc>
To:	Jarek Poplawski <jarkao2@...il.com>
CC:	David Miller <davem@...emloft.net>, johannes@...solutions.net,
	hidave.darkstar@...il.com, linux-kernel@...r.kernel.org,
	tglx@...utronix.de, linux-wireless@...r.kernel.org,
	linux-ppp@...r.kernel.org, netdev@...r.kernel.org, paulus@...ba.org
Subject: Re: NOHZ: local_softirq_pending 08

On 15.10.2009 19:53 Jarek Poplawski wrote:
> Jarek Poplawski wrote, On 10/15/2009 01:40 PM:
> 
>> On 12-10-2009 13:25, Tilman Schmidt wrote:

>>> I have encountered the message in the subject during a test of
>>> the Gigaset CAPI driver, and would like to determine whether
>>> it's a bug in the driver, a bug somewhere else, or no bug at
>>> all. The test scenario was PPP over ISDN with pppd+capiplugin.
>>> In an alternative scenario, also PPP over ISDN but with
>>> smpppd+capidrv, the message did not occur.

I'm sorry, I had confused the two cases. The message occurs in
the smpppd+capidrv scenario, not with pppd+capiplugin.

>>> Johannes' answer pointed me to the netif_rx() function.
>>> The Gigaset driver itself doesn't call that function at all.
>>> In the scenario where I saw the message, it was the SYNC_PPP
>>> line discipline that did.

This analysis was therefore wrong. It would be the netif_rx()
call towards the end of isdn_ppp_push_higher() in
drivers/isdn/i4l/isdn_ppp.c L1177.

>> Anyway, I agree with Michael Buesch there is no reason to waste time
>> for tracking all netif_rx vs netif_rx_ni uses, and it seems we could
>> avoid it by using the "proper" version of raise_softirq_irqoff() in
>> __napi_schedule(). Could anybody try if I'm not wrong?
>>
>>  net/core/dev.c |    2 +-
>>  1 files changed, 1 insertions(+), 1 deletions(-)
>>
>> diff --git a/net/core/dev.c b/net/core/dev.c
>> index 28b0b9e..7fc4009 100644
>> --- a/net/core/dev.c
>> +++ b/net/core/dev.c
>> @@ -2728,7 +2728,7 @@ void __napi_schedule(struct napi_struct *n)
>>  
>>  	local_irq_save(flags);
>>  	list_add_tail(&n->poll_list, &__get_cpu_var(softnet_data).poll_list);
>> -	__raise_softirq_irqoff(NET_RX_SOFTIRQ);
>> +	raise_softirq_irqoff(NET_RX_SOFTIRQ);
>>  	local_irq_restore(flags);
>>  }
>>  EXPORT_SYMBOL(__napi_schedule);

I have tested your patch and I can confirm that it fixes the messages.
I have not noticed any ill effects.

Thanks,
Tilman

-- 
Tilman Schmidt                    E-Mail: tilman@...p.cc
Bonn, Germany
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