linux-kernel - [net-next v4 1/2] tg3: Link IRQs to NAPI instances

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Message-Id: <20241009175509.31753-2-jdamato@fastly.com>
Date: Wed,  9 Oct 2024 17:55:08 +0000
From: Joe Damato <jdamato@...tly.com>
To: netdev@...r.kernel.org
Cc: michael.chan@...adcom.com,
	pavan.chebbi@...adcom.com,
	Joe Damato <jdamato@...tly.com>,
	Michael Chan <mchan@...adcom.com>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>,
	Paolo Abeni <pabeni@...hat.com>,
	linux-kernel@...r.kernel.org (open list)
Subject: [net-next v4 1/2] tg3: Link IRQs to NAPI instances

Link IRQs to NAPI instances with netif_napi_set_irq. This information
can be queried with the netdev-genl API.

Begin by testing my tg3 device in its default state: 1 TX queue and 4 RX
queues.

Compare the output of /proc/interrupts for my tg3 device with the output of
netdev-genl after applying this patch:

$ cat /proc/interrupts | grep eth0
343: [...] eth0-tx-0
344: [...] eth0-rx-1
345: [...] eth0-rx-2
346: [...] eth0-rx-3
347: [...] eth0-rx-4

As you can see above, tg3 has named the IRQs such that there is a
dedicated tx IRQ and 4 dedicated rx IRQs, for a total of 5 IRQs.

$ ./tools/net/ynl/cli.py --spec Documentation/netlink/specs/netdev.yaml \
			 --dump napi-get --json='{"ifindex": 2}'

[{'id': 8197, 'ifindex': 2, 'irq': 347},
 {'id': 8196, 'ifindex': 2, 'irq': 346},
 {'id': 8195, 'ifindex': 2, 'irq': 345},
 {'id': 8194, 'ifindex': 2, 'irq': 344},
 {'id': 8193, 'ifindex': 2, 'irq': 343}]

Netlink displays the same IRQs as above, noting that each is mapped to a
unique NAPI instance.

Now, reconfigure the NIC to have 4 TX queues and 4 RX queues:

$ sudo ethtool -L eth0 rx 4 tx 4
$ sudo ethtool -l eth0 | tail -5
Current hardware settings:
RX:		4
TX:		4
Other:		n/a
Combined:	n/a

Examine /proc/interrupts once again, noting that tg3 will now rename the
IRQs to suggest that they are combined tx and rx without allocating
additional IRQs, so the total IRQ count in /proc/interrupts is
unchanged:

343: [...] eth0-0
344: [...] eth0-txrx-1
345: [...] eth0-txrx-2
346: [...] eth0-txrx-3
347: [...] eth0-txrx-4

Check the output from netlink again:

$ ./tools/net/ynl/cli.py --spec Documentation/netlink/specs/netdev.yaml \
                         --dump napi-get --json='{"ifindex": 2}'
[{'id': 8973, 'ifindex': 2, 'irq': 347},
 {'id': 8972, 'ifindex': 2, 'irq': 346},
 {'id': 8971, 'ifindex': 2, 'irq': 345},
 {'id': 8970, 'ifindex': 2, 'irq': 344},
 {'id': 8969, 'ifindex': 2, 'irq': 343}]

Signed-off-by: Joe Damato <jdamato@...tly.com>
Reviewed-by: Pavan Chebbi <pavan.chebbi@...adcom.com>
---
 v4:
   - Updated commit message

 rfcv3:
   - wrapped the netif_napi_add call to 80 characters

 drivers/net/ethernet/broadcom/tg3.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/drivers/net/ethernet/broadcom/tg3.c b/drivers/net/ethernet/broadcom/tg3.c
index 378815917741..6564072b47ba 100644
--- a/drivers/net/ethernet/broadcom/tg3.c
+++ b/drivers/net/ethernet/broadcom/tg3.c
@@ -7413,9 +7413,11 @@ static void tg3_napi_init(struct tg3 *tp)
 {
 	int i;
 
-	netif_napi_add(tp->dev, &tp->napi[0].napi, tg3_poll);
-	for (i = 1; i < tp->irq_cnt; i++)
-		netif_napi_add(tp->dev, &tp->napi[i].napi, tg3_poll_msix);
+	for (i = 0; i < tp->irq_cnt; i++) {
+		netif_napi_add(tp->dev, &tp->napi[i].napi,
+			       i ? tg3_poll_msix : tg3_poll);
+		netif_napi_set_irq(&tp->napi[i].napi, tp->napi[i].irq_vec);
+	}
 }
 
 static void tg3_napi_fini(struct tg3 *tp)
-- 
2.25.1