Subject: [RFC] multiqueue changes

From: Eric Dumazet <[email-masked]>
Date: Thu, 08 Oct 2009 09:18:45 +0200

Say I have such non multiqueue device :

03:00.0 Ethernet controller: Broadcom Corporation NetXtreme II BCM5708S Gigabit Ethernet (rev 12)

Driver bnx2

This drivers does an alloc_etherdev_mq(sizeof(*bp), TX_MAX_RINGS),
regardless of real capabilities of the NIC.

Then, a bit later it does :

bp->dev->real_num_tx_queues = bp->num_tx_rings;  

(one in my non multiqueue case)

Now I have :

# tc -s -d qdisc show dev eth0
qdisc mq 0: root
 Sent 117693091 bytes 1542188 pkt (dropped 0, overlimits 0 requeues 0)
 backlog 0b 0p requeues 0
# tc -s -d class show dev eth0
class mq :1 root
 Sent 113935509 bytes 1492598 pkt (dropped 0, overlimits 0 requeues 0)
 backlog 0b 0p requeues 0
class mq :2 root
 Sent 0 bytes 0 pkt (dropped 0, overlimits 0 requeues 0)
 backlog 0b 0p requeues 0
class mq :3 root
 Sent 0 bytes 0 pkt (dropped 0, overlimits 0 requeues 0)
 backlog 0b 0p requeues 0
class mq :4 root
 Sent 0 bytes 0 pkt (dropped 0, overlimits 0 requeues 0)
 backlog 0b 0p requeues 0
class mq :5 root
 Sent 0 bytes 0 pkt (dropped 0, overlimits 0 requeues 0)
 backlog 0b 0p requeues 0
class mq :6 root
 Sent 0 bytes 0 pkt (dropped 0, overlimits 0 requeues 0)
 backlog 0b 0p requeues 0
class mq :7 root
 Sent 0 bytes 0 pkt (dropped 0, overlimits 0 requeues 0)
 backlog 0b 0p requeues 0
class mq :8 root
 Sent 0 bytes 0 pkt (dropped 0, overlimits 0 requeues 0)
 backlog 0b 0p requeues 0

While in previous kernels I had :

# tc -s -d qdisc show dev eth0
qdisc pfifo_fast 0: root bands 3 priomap  1 2 2 2 1 2 0 0 1 1 1 1 1 1 1 1
 Sent 26292963818 bytes 347139141 pkts (dropped 0, overlimits 0 requeues 0)
# tc -s -d class show dev eth0

So I lost the default pfifo_fast classification.

Just wondering if it could hurt some people.

Anyway, should we change bnx2/tg3 drivers so that single queue devices
have same default qdisc/class than before ?

eg :

diff --git a/drivers/net/bnx2.c b/drivers/net/bnx2.c
index 08cddb6..7cac205 100644
--- a/drivers/net/bnx2.c
+++ b/drivers/net/bnx2.c
@@ -6152,6 +6152,7 @@ bnx2_setup_int_mode(struct bnx2 *bp, int dis_msi)
 
 	bp->num_tx_rings = rounddown_pow_of_two(bp->irq_nvecs);
 	bp->dev->real_num_tx_queues = bp->num_tx_rings;
+	bp->dev->num_tx_queues = bp->dev->real_num_tx_queues;
 
 	bp->num_rx_rings = bp->irq_nvecs;
 }