[PATCH net-next] virtio-net: make napi_tx param easier to grasp

Subsystems: networking drivers, the rest, virtio net driver

STALE3344d

3 messages, 2 authors, 2017-08-21 · open the first message on its own page

[PATCH net-next] virtio-net: make napi_tx param easier to grasp

From: Koichiro Den <hidden>
Date: 2017-08-19 06:37:07

The module param napi_tx needs not to be writable for now since we do
not have any means of activating/deactivating it online, which seems to
be a low priority. Also make it clear that napi_tx is disabled when it
has been dynamically disabled behind the scenes.

Signed-off-by: Koichiro Den <redacted>
---
 drivers/net/virtio_net.c | 34 +++++++++++++++++++---------------
 1 file changed, 19 insertions(+), 15 deletions(-)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 4302f313d9a7..ea4e7ddcd377 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c

@@ -37,7 +37,7 @@ module_param(napi_weight, int, 0444);
 static bool csum = true, gso = true, napi_tx;
 module_param(csum, bool, 0444);
 module_param(gso, bool, 0444);
-module_param(napi_tx, bool, 0644);
+module_param(napi_tx, bool, 0444);
 
 /* FIXME: MTU in config. */
 #define GOOD_PACKET_LEN (ETH_HLEN + VLAN_HLEN + ETH_DATA_LEN)

@@ -1026,20 +1026,13 @@ static void virtnet_napi_enable(struct virtqueue *vq, struct napi_struct *napi)
 	local_bh_enable();
 }
 
-static void virtnet_napi_tx_enable(struct virtnet_info *vi,
-				   struct virtqueue *vq,
-				   struct napi_struct *napi)
+static void virtnet_napi_tx_enable(struct virtqueue *vq, struct napi_struct *napi)
 {
-	if (!napi->weight)
-		return;
-
-	/* Tx napi touches cachelines on the cpu handling tx interrupts. Only
-	 * enable the feature if this is likely affine with the transmit path.
-	 */
-	if (!vi->affinity_hint_set) {
+	if (!napi_tx)
 		napi->weight = 0;
+
+	if (!napi->weight)
 		return;
-	}
 
 	return virtnet_napi_enable(vq, napi);
 }

@@ -1179,13 +1172,19 @@ static int virtnet_open(struct net_device *dev)
 	struct virtnet_info *vi = netdev_priv(dev);
 	int i;
 
+	/* Tx napi touches cachelines on the cpu handling tx interrupts. Only
+	 * enable the feature if this is likely affine with the transmit path.
+	 */
+	if (!vi->affinity_hint_set)
+		napi_tx = false;
+
 	for (i = 0; i < vi->max_queue_pairs; i++) {
 		if (i < vi->curr_queue_pairs)
 			/* Make sure we have some buffers: if oom use wq. */
 			if (!try_fill_recv(vi, &vi->rq[i], GFP_KERNEL))
 				schedule_delayed_work(&vi->refill, 0);
 		virtnet_napi_enable(vi->rq[i].vq, &vi->rq[i].napi);
-		virtnet_napi_tx_enable(vi, vi->sq[i].vq, &vi->sq[i].napi);
+		virtnet_napi_tx_enable(vi->sq[i].vq, &vi->sq[i].napi);
 	}
 
 	return 0;

@@ -1890,6 +1889,12 @@ static int virtnet_restore_up(struct virtio_device *vdev)
 
 	virtio_device_ready(vdev);
 
+	/* Tx napi touches cachelines on the cpu handling tx interrupts. Only
+	 * enable the feature if this is likely affine with the transmit path.
+	 */
+	if (!vi->affinity_hint_set)
+		napi_tx = false;
+
 	if (netif_running(vi->dev)) {
 		for (i = 0; i < vi->curr_queue_pairs; i++)
 			if (!try_fill_recv(vi, &vi->rq[i], GFP_KERNEL))

@@ -1897,8 +1902,7 @@ static int virtnet_restore_up(struct virtio_device *vdev)
 
 		for (i = 0; i < vi->max_queue_pairs; i++) {
 			virtnet_napi_enable(vi->rq[i].vq, &vi->rq[i].napi);
-			virtnet_napi_tx_enable(vi, vi->sq[i].vq,
-					       &vi->sq[i].napi);
+			virtnet_napi_tx_enable(vi->sq[i].vq, &vi->sq[i].napi);
 		}
 	}

-- 
2.9.4

Re: [PATCH net-next] virtio-net: make napi_tx param easier to grasp

From: Willem de Bruijn <willemdebruijn.kernel@gmail.com>
Date: 2017-08-20 20:31:20

On Sat, Aug 19, 2017 at 2:37 AM, Koichiro Den [off-list ref] wrote:

The module param napi_tx needs not to be writable for now since we do
not have any means of activating/deactivating it online,

A virtio_net device inherits its napi tx mode from the global napi_tx flag
on device up. It is possible to change the parameter and bring a device
down/up to change the device mode.

quoted hunk

@@ -1179,13 +1172,19 @@ static int virtnet_open(struct net_device *dev)
        struct virtnet_info *vi = netdev_priv(dev);
        int i;

+       /* Tx napi touches cachelines on the cpu handling tx interrupts. Only
+        * enable the feature if this is likely affine with the transmit path.
+        */
+       if (!vi->affinity_hint_set)
+               napi_tx = false;
+

This disables napi globally if a specific device lacks affinity.

Re: [PATCH net-next] virtio-net: make napi_tx param easier to grasp

From: Koichiro Den <hidden>
Date: 2017-08-21 11:49:18

On Sun, 2017-08-20 at 16:30 -0400, Willem de Bruijn wrote:

On Sat, Aug 19, 2017 at 2:37 AM, Koichiro Den [off-list ref] wrote:

quoted

The module param napi_tx needs not to be writable for now since we do
not have any means of activating/deactivating it online,

A virtio_net device inherits its napi tx mode from the global napi_tx flag
on device up. It is possible to change the parameter and bring a device
down/up to change the device mode.

quoted

@@ -1179,13 +1172,19 @@ static int virtnet_open(struct net_device *dev)

        struct virtnet_info *vi = netdev_priv(dev);
        int i;

+       /* Tx napi touches cachelines on the cpu handling tx interrupts.
Only
+        * enable the feature if this is likely affine with the transmit
path.
+        */
+       if (!vi->affinity_hint_set)
+               napi_tx = false;
+

This disables napi globally if a specific device lacks affinity.

Now I see this is not appropriate since it just represents whether or not TX
napi is available, not that whether or not it is being turned on or off on a
particular device. Thank you.

To be honest I hoped to make it possible to see which mode it is currently
running on with ease, but I guess it's not nice to accomplish it with net sysfs
nor ethtool or whatever because it seems not much generic matter.

Thanks.

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