netdev - Re: [PATCH net-next v4 10/10] tsnep: Support XDP BPF program setup

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Date:   Tue, 10 Jan 2023 22:38:04 +0100
From:   Gerhard Engleder <gerhard@...leder-embedded.com>
To:     Alexander H Duyck <alexander.duyck@...il.com>,
        netdev@...r.kernel.org
Cc:     davem@...emloft.net, kuba@...nel.org, edumazet@...gle.com,
        pabeni@...hat.com
Subject: Re: [PATCH net-next v4 10/10] tsnep: Support XDP BPF program setup

On 10.01.23 18:33, Alexander H Duyck wrote:
> On Mon, 2023-01-09 at 20:15 +0100, Gerhard Engleder wrote:
>> Implement setup of BPF programs for XDP RX path with command
>> XDP_SETUP_PROG of ndo_bpf(). This is the final step for XDP RX path
>> support.
>>
>> tsnep_netdev_close() is called directly during BPF program setup. Add
>> netif_carrier_off() and netif_tx_stop_all_queues() calls to signal to
>> network stack that device is down. Otherwise network stack would
>> continue transmitting pakets.
>>
>> Return value of tsnep_netdev_open() is not checked during BPF program
>> setup like in other drivers. Forwarding the return value would result in
>> a bpf_prog_put() call in dev_xdp_install(), which would make removal of
>> BPF program necessary.
>>
>> If tsnep_netdev_open() fails during BPF program setup, then the network
>> stack would call tsnep_netdev_close() anyway. Thus, tsnep_netdev_close()
>> checks now if device is already down.
>>
>> Additionally remove $(tsnep-y) from $(tsnep-objs) because it is added
>> automatically.
>>
>> Test results with A53 1.2GHz:
>>
>> XDP_DROP (samples/bpf/xdp1)
>> proto 17:     883878 pkt/s
>>
>> XDP_TX (samples/bpf/xdp2)
>> proto 17:     255693 pkt/s
>>
>> XDP_REDIRECT (samples/bpf/xdpsock)
>>   sock0@...2:0 rxdrop xdp-drv
>>                     pps            pkts           1.00
>> rx                 855,582        5,404,523
>> tx                 0              0
>>
>> XDP_REDIRECT (samples/bpf/xdp_redirect)
>> eth2->eth1         613,267 rx/s   0 err,drop/s   613,272 xmit/s
>>
>> Signed-off-by: Gerhard Engleder <gerhard@...leder-embedded.com>
>> ---
>>   drivers/net/ethernet/engleder/Makefile     |  2 +-
>>   drivers/net/ethernet/engleder/tsnep.h      |  6 +++++
>>   drivers/net/ethernet/engleder/tsnep_main.c | 25 ++++++++++++++++---
>>   drivers/net/ethernet/engleder/tsnep_xdp.c  | 29 ++++++++++++++++++++++
>>   4 files changed, 58 insertions(+), 4 deletions(-)
>>   create mode 100644 drivers/net/ethernet/engleder/tsnep_xdp.c
>>
>>
> 
> <...>
> 
>> --- a/drivers/net/ethernet/engleder/tsnep_main.c
>> +++ b/drivers/net/ethernet/engleder/tsnep_main.c
>> @@ -1373,7 +1373,7 @@ static void tsnep_free_irq(struct tsnep_queue *queue, bool first)
>>   	memset(queue->name, 0, sizeof(queue->name));
>>   }
>>   
>> -static int tsnep_netdev_open(struct net_device *netdev)
>> +int tsnep_netdev_open(struct net_device *netdev)
>>   {
>>   	struct tsnep_adapter *adapter = netdev_priv(netdev);
>>   	int tx_queue_index = 0;
>> @@ -1436,6 +1436,8 @@ static int tsnep_netdev_open(struct net_device *netdev)
>>   		tsnep_enable_irq(adapter, adapter->queue[i].irq_mask);
>>   	}
>>   
>> +	netif_tx_start_all_queues(adapter->netdev);
>> +
>>   	clear_bit(__TSNEP_DOWN, &adapter->state);
>>   
>>   	return 0;
>> @@ -1457,12 +1459,16 @@ static int tsnep_netdev_open(struct net_device *netdev)
>>   	return retval;
>>   }
>>   
>> -static int tsnep_netdev_close(struct net_device *netdev)
>> +int tsnep_netdev_close(struct net_device *netdev)
>>   {
>>   	struct tsnep_adapter *adapter = netdev_priv(netdev);
>>   	int i;
>>   
>> -	set_bit(__TSNEP_DOWN, &adapter->state);
>> +	if (test_and_set_bit(__TSNEP_DOWN, &adapter->state))
>> +		return 0;
>> +
>> +	netif_carrier_off(netdev);
>> +	netif_tx_stop_all_queues(netdev);
>>   
> 
> As I called out earlier the __TSNEP_DOWN is just !IFF_UP so you don't
> need that bit.
> 
> The fact that netif_carrier_off is here also points out the fact that
> the code in the Tx path isn't needed regarding __TSNEP_DOWN and you can
> probably just check netif_carrier_ok if you need the check.

tsnep_netdev_close() is called directly during bpf prog setup (see
tsnep_xdp_setup_prog() in this commit). If the following
tsnep_netdev_open() call fails, then this flag signals that the device
is already down and nothing needs to be cleaned up if
tsnep_netdev_close() is called later (because IFF_UP is still set).

Thanks for the review!

Gerhard