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

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Message-ID: <87eczt3vty.fsf@kurt.kurt.home>
Date: Thu, 20 Feb 2025 08:43:21 +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 Wed Feb 19 2025, Joe Damato wrote:
> On Wed, Feb 19, 2025 at 08:41:01AM +0100, Kurt Kanzenbach wrote:
>> 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.
>
> OK, I spent a bit of time tracing through the paths in the igb
> source. I think the v1 feedback I sent identified all the RTNL
> paths, but: 
>   - I am not an igb expert
>   - I don't have a device to test this on

Intel i210 is one of the supported cards by igb driver. These are
relatively cheap (20-30 Euro/$) and easy to get hands on.

>   - It is certainly possible I missed a path in my v1 analysis
>
> The above said, as far as I can tell this patch seems fine, so:
>
> Acked-by: Joe Damato <jdamato@...tly.com>

Thanks.

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