netdev - Re: [PATCH][net-next] gianfar: Fix reported sent bytes to BQL for Tx timestamping

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Message-ID: <517E8354.1010503@freescale.com>
Date:	Mon, 29 Apr 2013 17:27:32 +0300
From:	Claudiu Manoil <claudiu.manoil@...escale.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
CC:	<netdev@...r.kernel.org>,
	Paul Gortmaker <paul.gortmaker@...driver.com>,
	"David S. Miller" <davem@...emloft.net>
Subject: Re: [PATCH][net-next] gianfar: Fix reported sent bytes to BQL for
 Tx timestamping

Hi,

Unfortunately fixing this the other way around would imply changes
in both xmit and clean_tx, and additional overhead in clean_tx.
On xmit skb->len gets incremented with FCB_LEN and/or TXPAL_LEN,
on a case by case basis. This would imply to add extra checks on
clean_tx to identify whether only FCB_LEN has been added, or
FCB+TXPAL or neither, all these just to report the bytes on wire
for BQL.
Does BQL really need to measure the bytes-on-wire or the bytes consumed
for buffering?

Thanks,
Claudiu

On 4/29/2013 4:53 PM, Eric Dumazet wrote:
> On Mon, 2013-04-29 at 15:57 +0300, Claudiu Manoil wrote:
>> When Tx timestamping is enabled the number of sent bytes reported
>> to BQL via tx_completed_queue() falls short by GMAC_FCB_LEN +
>> GMAC_TXPAL_LEN than the number of bytes reported via tx_sent_queue()
>> on xmit. This leads to BQL stopping transmission errorneously followed
>> by tx timeout firing.
>>
>> This fixes the amount of sent bytes reported to BQL on clean_tx_ring
>> to match the amount reported on xmit, when Tx timestamping enabled.
>>
>> Signed-off-by: Claudiu Manoil <claudiu.manoil@...escale.com>
>> ---
>>   drivers/net/ethernet/freescale/gianfar.c | 1 +
>>   1 file changed, 1 insertion(+)
>>
>> diff --git a/drivers/net/ethernet/freescale/gianfar.c b/drivers/net/ethernet/freescale/gianfar.c
>> index 2375a01..0d26a8b 100644
>> --- a/drivers/net/ethernet/freescale/gianfar.c
>> +++ b/drivers/net/ethernet/freescale/gianfar.c
>> @@ -2539,6 +2539,7 @@ static void gfar_clean_tx_ring(struct gfar_priv_tx_q *tx_queue)
>>   			skb_tstamp_tx(skb, &shhwtstamps);
>>   			bdp->lstatus &= BD_LFLAG(TXBD_WRAP);
>>   			bdp = next;
>> +			bytes_sent += GMAC_FCB_LEN + GMAC_TXPAL_LEN;
>>   		}
>>
>>   		bdp->lstatus &= BD_LFLAG(TXBD_WRAP);
>
> Technically speaking these bytes are not sent to the wire.
>
> I would rather fix gfar_start_xmit() to give to netdev_tx_sent_queue()
> call the correct amount of bytes on wire, to be consistent with other
> drivers.
>
>
>
>
>


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