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Date:   Wed, 12 May 2021 10:53:37 +0300
From:   Gatis Peisenieks <gatis@mikrotik.com>
To:     Eric Dumazet <eric.dumazet@gmail.com>
Cc:     chris.snook@gmail.com, davem@davemloft.net, kuba@kernel.org,
        hkallweit1@gmail.com, jesse.brandeburg@intel.com,
        dchickles@marvell.com, tully@mikrotik.com, netdev@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH net-next 2/4] atl1c: improve performance by avoiding
 unnecessary pcie writes on xmit
In-Reply-To: <217ba8c9-ab09-46be-3e49-149f810e72fd@gmail.com>
References: <20210511190518.8901-1-gatis@mikrotik.com>
 <20210511190518.8901-3-gatis@mikrotik.com>
 <217ba8c9-ab09-46be-3e49-149f810e72fd@gmail.com>
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On 2021-05-12 00:39, Eric Dumazet wrote:
>> @@ -2270,8 +2272,11 @@ static netdev_tx_t atl1c_xmit_frame(struct 
>> sk_buff *skb,
>>  		atl1c_tx_rollback(adapter, tpd, type);
>>  		dev_kfree_skb_any(skb);
>>  	} else {
>> -		netdev_sent_queue(adapter->netdev, skb->len);
>> -		atl1c_tx_queue(adapter, skb, tpd, type);
>> +		bool more = netdev_xmit_more();
>> +
>> +		__netdev_sent_queue(adapter->netdev, skb->len, more);
> 
> 
> This is probably buggy.
> 
> You must check and use the return code of this function,
> as in :
> 
> 	bool door_bell = __netdev_sent_queue(adapter->netdev, skb->len,
> netdev_xmit_more());
> 
> 	if (door_bell)
> 		atl1c_tx_queue(adapter, type);
> 

Eric, thank you for taking your time to look at this!

You are correct, tx queue can get stopped in __netdev_sent_queue
and if there were more packets coming the submit to HW would be
missed / unnecessarily delayed.


> 
>> +		if (!more)
>> +			atl1c_tx_queue(adapter, type);
>>  	}
>> 
>>  	return NETDEV_TX_OK;
>>