netdev - Re: BQL support in gianfar causes network hiccup

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Message-ID: <59220.62.16.236.213.1378236817.squirrel@webmail.m5.itpays.net>
Date:	Tue, 3 Sep 2013 21:33:37 +0200 (CEST)
From:	Per Dalén <per.dalen@...eartv.com>
To:	"Claudiu Manoil" <claudiu.manoil@...escale.com>
Cc:	"Eric Dumazet" <eric.dumazet@...il.com>,
	Per DalÃ©n <per.dalen@...eartv.com>,
	netdev@...r.kernel.org
Subject: Re: BQL support in gianfar causes network hiccup

>
>
> On 9/3/2013 6:42 PM, Eric Dumazet wrote:
>> On Tue, 2013-09-03 at 09:55 +0200, Per DalÃ©n wrote:
>>
>>> Yes, it's weird. The only reason I removed the BQL commit
>>> (d8a0f1b0af67679bba886784de10d8c21acc4e0e) was because the error Tino
>>> Keitel had was the similar as mine.
>>
>>
>> I suspect a genuine race in this driver. BQL only makes this race happen
>> more often.
>>
>> gfar_poll_sq() has the following :
>>
>> /* run Tx cleanup to completion */
>> if (tx_queue->tx_skbuff[tx_queue->skb_dirtytx])
>>          gfar_clean_tx_ring(tx_queue);
>>
>> While gfar_poll() has a different method :
>>
>> if (tx_queue->tx_skbuff[tx_queue->skb_dirtytx]) {
>>      gfar_clean_tx_ring(tx_queue);
>>      has_tx_work = 1;
>> }
>>
>> Note the has_tx_work use in gfar_poll() only.
>>
>> Note that memory barriers seems to be missing.
>>
>> 1) In your cases, is it gfar_poll_sq() or gfar_poll() that is used ?
>>
>
> It's gfar_poll_sq(). P2020 single Tx/Rx queues.
>
> I'm also seeing carrier errors and packet collisions in this case
> (100/Half link).
>
>> 2) Is the bug happening if only one CPU is used ?
>>
>
> I didn't try this. Maybe Per did?
>

I use both CPUs.

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