netdev - Re: [PATCH iwl-next v2 2/4] igb: Link queues to NAPI instances

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Message-ID: <875xl62xgy.fsf@kurt.kurt.home>
Date: Wed, 19 Feb 2025 08:41:01 +0100
From: Kurt Kanzenbach <kurt@...utronix.de>
To: Joe Damato <jdamato@...tly.com>
Cc: Tony Nguyen <anthony.l.nguyen@...el.com>, Przemek Kitszel
 <przemyslaw.kitszel@...el.com>, Andrew Lunn <andrew+netdev@...n.ch>,
 "David S. Miller" <davem@...emloft.net>, Eric Dumazet
 <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni
 <pabeni@...hat.com>, Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
 Gerhard Engleder <gerhard@...leder-embedded.com>,
 intel-wired-lan@...ts.osuosl.org, netdev@...r.kernel.org
Subject: Re: [PATCH iwl-next v2 2/4] igb: Link queues to NAPI instances

On Tue Feb 18 2025, Joe Damato wrote:
> On Mon, Feb 17, 2025 at 12:31:22PM +0100, Kurt Kanzenbach wrote:
>> Link queues to NAPI instances via netdev-genl API. This is required to use
>> XDP/ZC busy polling. See commit 5ef44b3cb43b ("xsk: Bring back busy polling
>> support") for details.
>> 
>> This also allows users to query the info with netlink:
>> 
>> |$ ./tools/net/ynl/pyynl/cli.py --spec Documentation/netlink/specs/netdev.yaml \
>> |                               --dump queue-get --json='{"ifindex": 2}'
>> |[{'id': 0, 'ifindex': 2, 'napi-id': 8201, 'type': 'rx'},
>> | {'id': 1, 'ifindex': 2, 'napi-id': 8202, 'type': 'rx'},
>> | {'id': 2, 'ifindex': 2, 'napi-id': 8203, 'type': 'rx'},
>> | {'id': 3, 'ifindex': 2, 'napi-id': 8204, 'type': 'rx'},
>> | {'id': 0, 'ifindex': 2, 'napi-id': 8201, 'type': 'tx'},
>> | {'id': 1, 'ifindex': 2, 'napi-id': 8202, 'type': 'tx'},
>> | {'id': 2, 'ifindex': 2, 'napi-id': 8203, 'type': 'tx'},
>> | {'id': 3, 'ifindex': 2, 'napi-id': 8204, 'type': 'tx'}]
>> 
>> Add rtnl locking to PCI error handlers, because netif_queue_set_napi()
>> requires the lock held.
>> 
>> While at __igb_open() use RCT coding style.
>> 
>> Signed-off-by: Kurt Kanzenbach <kurt@...utronix.de>
>> ---
>>  drivers/net/ethernet/intel/igb/igb.h      |  2 ++
>>  drivers/net/ethernet/intel/igb/igb_main.c | 43 +++++++++++++++++++++++++++----
>>  drivers/net/ethernet/intel/igb/igb_xsk.c  |  2 ++
>>  3 files changed, 42 insertions(+), 5 deletions(-)
>
> [...]
>
>> @@ -9737,16 +9765,21 @@ static void igb_io_resume(struct pci_dev *pdev)
>>  	struct net_device *netdev = pci_get_drvdata(pdev);
>>  	struct igb_adapter *adapter = netdev_priv(netdev);
>>  
>> +	rtnl_lock();
>>  	if (netif_running(netdev)) {
>>  		if (!test_bit(__IGB_DOWN, &adapter->state)) {
>>  			dev_dbg(&pdev->dev, "Resuming from non-fatal error, do nothing.\n");
>> +			rtnl_unlock();
>>  			return;
>>  		}
>> +
>>  		if (igb_up(adapter)) {
>>  			dev_err(&pdev->dev, "igb_up failed after reset\n");
>> +			rtnl_unlock();
>>  			return;
>>  		}
>>  	}
>> +	rtnl_unlock();
>
> Does RTNL need to be held when calling netif_running()? If not, you
> could probably reduce the size of the section under the lock a bit?

All the other instances in the driver guard the netif_running(), too.

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