netdev - [PATCH net-next] virtio-net: enable multiqueue by default

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Date:   Fri, 25 Nov 2016 12:37:26 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Cc:     Jason Wang <jasowang@...hat.com>,
        Hannes Frederic Sowa <hannes@...hat.com>,
        "Michael S . Tsirkin" <mst@...hat.com>,
        Neil Horman <nhorman@...hat.com>,
        Jeremy Eder <jeder@...hat.com>,
        Marko Myllynen <myllynen@...hat.com>,
        Maxime Coquelin <maxime.coquelin@...hat.com>
Subject: [PATCH net-next] virtio-net: enable multiqueue by default

We use single queue even if multiqueue is enabled and let admin to
enable it through ethtool later. This is used to avoid possible
regression (small packet TCP stream transmission). But looks like an
overkill since:

- single queue user can disable multiqueue when launching qemu
- brings extra troubles for the management since it needs extra admin
  tool in guest to enable multiqueue
- multiqueue performs much better than single queue in most of the
  cases

So this patch enables multiqueue by default: if #queues is less than or
equal to #vcpu, enable as much as queue pairs; if #queues is greater
than #vcpu, enable #vcpu queue pairs.

Cc: Hannes Frederic Sowa <hannes@...hat.com>
Cc: Michael S. Tsirkin <mst@...hat.com>
Cc: Neil Horman <nhorman@...hat.com>
Cc: Jeremy Eder <jeder@...hat.com>
Cc: Marko Myllynen <myllynen@...hat.com>
Cc: Maxime Coquelin <maxime.coquelin@...hat.com>
Signed-off-by: Jason Wang <jasowang@...hat.com>
---
 drivers/net/virtio_net.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index d4ac7a6..a21d93a 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -1886,8 +1886,11 @@ static int virtnet_probe(struct virtio_device *vdev)
 	if (vi->any_header_sg)
 		dev->needed_headroom = vi->hdr_len;
 
-	/* Use single tx/rx queue pair as default */
-	vi->curr_queue_pairs = 1;
+	/* Enable multiqueue by default */
+	if (num_online_cpus() >= max_queue_pairs)
+		vi->curr_queue_pairs = max_queue_pairs;
+	else
+		vi->curr_queue_pairs = num_online_cpus();
 	vi->max_queue_pairs = max_queue_pairs;
 
 	/* Allocate/initialize the rx/tx queues, and invoke find_vqs */
@@ -1918,6 +1921,8 @@ static int virtnet_probe(struct virtio_device *vdev)
 		goto free_unregister_netdev;
 	}
 
+	virtnet_set_affinity(vi);
+
 	/* Assume link up if device can't report link status,
 	   otherwise get link status from config. */
 	if (virtio_has_feature(vi->vdev, VIRTIO_NET_F_STATUS)) {
-- 
2.7.4