netdev - Re: [RFC net-next 2/2] igc: Link queues to NAPI instances

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Message-ID: <87msjg46lw.fsf@kurt.kurt.home>
Date: Mon, 07 Oct 2024 11:14:51 +0200
From: Kurt Kanzenbach <kurt@...utronix.de>
To: Joe Damato <jdamato@...tly.com>, netdev@...r.kernel.org
Cc: Joe Damato <jdamato@...tly.com>, Tony Nguyen
 <anthony.l.nguyen@...el.com>, Przemek Kitszel
 <przemyslaw.kitszel@...el.com>, "David S. Miller" <davem@...emloft.net>,
 Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>,
 Paolo Abeni <pabeni@...hat.com>, "moderated list:INTEL ETHERNET DRIVERS"
 <intel-wired-lan@...ts.osuosl.org>, open list
 <linux-kernel@...r.kernel.org>
Subject: Re: [RFC net-next 2/2] igc: Link queues to NAPI instances

Hi Joe,

On Thu Oct 03 2024, Joe Damato wrote:
> Link queues to NAPI instances via netdev-genl API so that users can
> query this information with netlink:
>
> $ ./tools/net/ynl/cli.py --spec Documentation/netlink/specs/netdev.yaml \
>                          --dump queue-get --json='{"ifindex": 2}'
>
> [{'id': 0, 'ifindex': 2, 'napi-id': 8193, 'type': 'rx'},
>  {'id': 1, 'ifindex': 2, 'napi-id': 8194, 'type': 'rx'},
>  {'id': 2, 'ifindex': 2, 'napi-id': 8195, 'type': 'rx'},
>  {'id': 3, 'ifindex': 2, 'napi-id': 8196, 'type': 'rx'},
>  {'id': 0, 'ifindex': 2, 'napi-id': 8193, 'type': 'tx'},
>  {'id': 1, 'ifindex': 2, 'napi-id': 8194, 'type': 'tx'},
>  {'id': 2, 'ifindex': 2, 'napi-id': 8195, 'type': 'tx'},
>  {'id': 3, 'ifindex': 2, 'napi-id': 8196, 'type': 'tx'}]
>
> Since igc uses only combined queues, you'll note that the same NAPI ID
> is present for both rx and tx queues at the same index, for example
> index 0:
>
> {'id': 0, 'ifindex': 2, 'napi-id': 8193, 'type': 'rx'},
> {'id': 0, 'ifindex': 2, 'napi-id': 8193, 'type': 'tx'},
>
> Signed-off-by: Joe Damato <jdamato@...tly.com>
> ---
>  drivers/net/ethernet/intel/igc/igc_main.c | 30 ++++++++++++++++++++---
>  1 file changed, 26 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/net/ethernet/intel/igc/igc_main.c b/drivers/net/ethernet/intel/igc/igc_main.c
> index 7964bbedb16c..b3bd5bf29fa7 100644
> --- a/drivers/net/ethernet/intel/igc/igc_main.c
> +++ b/drivers/net/ethernet/intel/igc/igc_main.c
> @@ -4955,6 +4955,7 @@ static int igc_sw_init(struct igc_adapter *adapter)
>  void igc_up(struct igc_adapter *adapter)
>  {
>  	struct igc_hw *hw = &adapter->hw;
> +	struct napi_struct *napi;
>  	int i = 0;
>  
>  	/* hardware has been reset, we need to reload some things */
> @@ -4962,8 +4963,17 @@ void igc_up(struct igc_adapter *adapter)
>  
>  	clear_bit(__IGC_DOWN, &adapter->state);
>  
> -	for (i = 0; i < adapter->num_q_vectors; i++)
> -		napi_enable(&adapter->q_vector[i]->napi);
> +	for (i = 0; i < adapter->num_q_vectors; i++) {
> +		napi = &adapter->q_vector[i]->napi;
> +		napi_enable(napi);
> +		/* igc only supports combined queues, so link each NAPI to both
> +		 * TX and RX
> +		 */

igc has IGC_FLAG_QUEUE_PAIRS. For example there may be 2 queues
configured, but 4 vectors active (and 4 IRQs). Is your patch working
with that?  Can be tested easily with `ethtool -L <inf> combined 2` or
by booting with only 2 CPUs.

Thanks,
Kurt

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