netdev - Re: [PATCH net-next 3/3] r8169: use new macro netif_subqueue_completed

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Date:   Thu, 13 Apr 2023 21:36:34 +0200
From:   Heiner Kallweit <hkallweit1@...il.com>
To:     Jacob Keller <jacob.e.keller@...el.com>,
        Jakub Kicinski <kuba@...nel.org>,
        David Miller <davem@...emloft.net>,
        Paolo Abeni <pabeni@...hat.com>,
        Eric Dumazet <edumazet@...gle.com>,
        Realtek linux nic maintainers <nic_swsd@...ltek.com>
Cc:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [PATCH net-next 3/3] r8169: use new macro
 netif_subqueue_completed_wake in the tx cleanup path

On 13.04.2023 21:25, Jacob Keller wrote:
> 
> 
> On 4/13/2023 12:16 PM, Heiner Kallweit wrote:
>> Use new net core macro netif_subqueue_completed_wake to simplify
>> the code of the tx cleanup path.
>>
>> Signed-off-by: Heiner Kallweit <hkallweit1@...il.com>
>> ---
>>  drivers/net/ethernet/realtek/r8169_main.c | 16 ++++------------
>>  1 file changed, 4 insertions(+), 12 deletions(-)
>>
>> diff --git a/drivers/net/ethernet/realtek/r8169_main.c b/drivers/net/ethernet/realtek/r8169_main.c
>> index 3f0b78fd9..5cfdb60ab 100644
>> --- a/drivers/net/ethernet/realtek/r8169_main.c
>> +++ b/drivers/net/ethernet/realtek/r8169_main.c
>> @@ -4372,20 +4372,12 @@ static void rtl_tx(struct net_device *dev, struct rtl8169_private *tp,
>>  	}
>>  
>>  	if (tp->dirty_tx != dirty_tx) {
>> -		netdev_completed_queue(dev, pkts_compl, bytes_compl);
>>  		dev_sw_netstats_tx_add(dev, pkts_compl, bytes_compl);
>> +		WRITE_ONCE(tp->dirty_tx, dirty_tx);
>>  
>> -		/* Sync with rtl8169_start_xmit:
>> -		 * - publish dirty_tx ring index (write barrier)
>> -		 * - refresh cur_tx ring index and queue status (read barrier)
>> -		 * May the current thread miss the stopped queue condition,
>> -		 * a racing xmit thread can only have a right view of the
>> -		 * ring status.
>> -		 */
>> -		smp_store_mb(tp->dirty_tx, dirty_tx);
> 
> 
> We used to use a smp_store_mb here, but now its safe to just WRITE_ONCE?
> Assuming that's correct:
> 
netdev_completed_queue() has a smp_mb() and is called from
netif_subqueue_completed_wake(). So it's supposed to be safe.

> Reviewed-by: Jacob Keller <jacob.e.keller@...el.com>
> 
>> -		if (netif_queue_stopped(dev) &&
>> -		    rtl_tx_slots_avail(tp) >= R8169_TX_START_THRS)
>> -			netif_wake_queue(dev);
>> +		netif_subqueue_completed_wake(dev, 0, pkts_compl, bytes_compl,
>> +					      rtl_tx_slots_avail(tp),
>> +					      R8169_TX_START_THRS);
>>  		/*
>>  		 * 8168 hack: TxPoll requests are lost when the Tx packets are
>>  		 * too close. Let's kick an extra TxPoll request when a burst