netdev - Re: net: Detect drivers that reschedule NAPI and exhaust budget

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Message-Id: <20141219.214000.819506179607476836.davem@davemloft.net>
Date:	Fri, 19 Dec 2014 21:40:00 -0500 (EST)
From:	David Miller <davem@...emloft.net>
To:	eric.dumazet@...il.com
Cc:	herbert@...dor.apana.org.au, david.vrabel@...rix.com,
	netdev@...r.kernel.org, xen-devel@...ts.xenproject.org,
	konrad.wilk@...cle.com, boris.ostrovsky@...cle.com,
	edumazet@...gle.com
Subject: Re: net: Detect drivers that reschedule NAPI and exhaust budget

From: Eric Dumazet <eric.dumazet@...il.com>
Date: Fri, 19 Dec 2014 17:34:48 -0800

>> @@ -4620,7 +4620,11 @@ static void net_rx_action(struct softirq_action *h)
>>  					 */
>>  					napi_gro_flush(n, HZ >= 1000);
>>  				}
>> -				list_add_tail(&n->poll_list, &repoll);
>> +				/* Some drivers may have called napi_schedule
>> +				 * prior to exhausting their budget.
>> +				 */
>> +				if (!WARN_ON_ONCE(!list_empty(&n->poll_list)))
>> +					list_add_tail(&n->poll_list, &repoll);
>>  			}
>>  		}
>>  
> 
> I do not think stack trace will point to the buggy driver ?
> 
> IMO it would be better to print a single line with the netdev name ?

Right, we are already back from the poll routine and will just end
up seeing the call trace leading to the software interrupt.

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