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xen-netfront: Add support for multiple queues
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Build on the refactoring of the previous patch to implement multiple
queues between xen-netfront and xen-netback.

Check XenStore for multi-queue support, and set up the rings and event
channels accordingly.

Write ring references and event channels to XenStore in a queue
hierarchy if appropriate, or flat when using only one queue.

Update the xennet_select_queue() function to choose the queue on which
to transmit a packet based on the skb hash result.

Signed-off-by: Andrew J. Bennieston <andrew.bennieston@citrix.com>
Acked-by: Wei Liu <wei.liu2@citrix.com>
Reviewed-by: David Vrabel <david.vrabel@citrix.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
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Andrew J. Bennieston authored and David S. Miller committed Jun 4, 2014
1 parent 2688fcb commit 50ee606
Showing 1 changed file with 134 additions and 36 deletions.
170 changes: 134 additions & 36 deletions drivers/net/xen-netfront.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -57,6 +57,12 @@
#include <xen/interface/memory.h>
#include <xen/interface/grant_table.h>

/* Module parameters */
static unsigned int xennet_max_queues;
module_param_named(max_queues, xennet_max_queues, uint, 0644);
MODULE_PARM_DESC(max_queues,
"Maximum number of queues per virtual interface");

static const struct ethtool_ops xennet_ethtool_ops;

struct netfront_cb {
Expand Down Expand Up @@ -565,10 +571,22 @@ static int xennet_count_skb_frag_slots(struct sk_buff *skb)
return pages;
}

static u16 xennet_select_queue(struct net_device *dev, struct sk_buff *skb)
static u16 xennet_select_queue(struct net_device *dev, struct sk_buff *skb,
void *accel_priv, select_queue_fallback_t fallback)
{
/* Stub for later implementation of queue selection */
return 0;
unsigned int num_queues = dev->real_num_tx_queues;
u32 hash;
u16 queue_idx;

/* First, check if there is only one queue */
if (num_queues == 1) {
queue_idx = 0;
} else {
hash = skb_get_hash(skb);
queue_idx = hash % num_queues;
}

return queue_idx;
}

static int xennet_start_xmit(struct sk_buff *skb, struct net_device *dev)
Expand Down Expand Up @@ -1316,7 +1334,7 @@ static struct net_device *xennet_create_dev(struct xenbus_device *dev)
struct net_device *netdev;
struct netfront_info *np;

netdev = alloc_etherdev_mq(sizeof(struct netfront_info), 1);
netdev = alloc_etherdev_mq(sizeof(struct netfront_info), xennet_max_queues);
if (!netdev)
return ERR_PTR(-ENOMEM);

Expand Down Expand Up @@ -1687,6 +1705,88 @@ static int xennet_init_queue(struct netfront_queue *queue)
return err;
}

static int write_queue_xenstore_keys(struct netfront_queue *queue,
struct xenbus_transaction *xbt, int write_hierarchical)
{
/* Write the queue-specific keys into XenStore in the traditional
* way for a single queue, or in a queue subkeys for multiple
* queues.
*/
struct xenbus_device *dev = queue->info->xbdev;
int err;
const char *message;
char *path;
size_t pathsize;

/* Choose the correct place to write the keys */
if (write_hierarchical) {
pathsize = strlen(dev->nodename) + 10;
path = kzalloc(pathsize, GFP_KERNEL);
if (!path) {
err = -ENOMEM;
message = "out of memory while writing ring references";
goto error;
}
snprintf(path, pathsize, "%s/queue-%u",
dev->nodename, queue->id);
} else {
path = (char *)dev->nodename;
}

/* Write ring references */
err = xenbus_printf(*xbt, path, "tx-ring-ref", "%u",
queue->tx_ring_ref);
if (err) {
message = "writing tx-ring-ref";
goto error;
}

err = xenbus_printf(*xbt, path, "rx-ring-ref", "%u",
queue->rx_ring_ref);
if (err) {
message = "writing rx-ring-ref";
goto error;
}

/* Write event channels; taking into account both shared
* and split event channel scenarios.
*/
if (queue->tx_evtchn == queue->rx_evtchn) {
/* Shared event channel */
err = xenbus_printf(*xbt, path,
"event-channel", "%u", queue->tx_evtchn);
if (err) {
message = "writing event-channel";
goto error;
}
} else {
/* Split event channels */
err = xenbus_printf(*xbt, path,
"event-channel-tx", "%u", queue->tx_evtchn);
if (err) {
message = "writing event-channel-tx";
goto error;
}

err = xenbus_printf(*xbt, path,
"event-channel-rx", "%u", queue->rx_evtchn);
if (err) {
message = "writing event-channel-rx";
goto error;
}
}

if (write_hierarchical)
kfree(path);
return 0;

error:
if (write_hierarchical)
kfree(path);
xenbus_dev_fatal(dev, err, "%s", message);
return err;
}

/* Common code used when first setting up, and when resuming. */
static int talk_to_netback(struct xenbus_device *dev,
struct netfront_info *info)
Expand All @@ -1696,11 +1796,19 @@ static int talk_to_netback(struct xenbus_device *dev,
int err;
unsigned int feature_split_evtchn;
unsigned int i = 0;
unsigned int max_queues = 0;
struct netfront_queue *queue = NULL;
unsigned int num_queues = 1;

info->netdev->irq = 0;

/* Check if backend supports multiple queues */
err = xenbus_scanf(XBT_NIL, info->xbdev->otherend,
"multi-queue-max-queues", "%u", &max_queues);
if (err < 0)
max_queues = 1;
num_queues = min(max_queues, xennet_max_queues);

/* Check feature-split-event-channels */
err = xenbus_scanf(XBT_NIL, info->xbdev->otherend,
"feature-split-event-channels", "%u",
Expand Down Expand Up @@ -1765,49 +1873,35 @@ static int talk_to_netback(struct xenbus_device *dev,
}

again:
queue = &info->queues[0]; /* Use first queue only */

err = xenbus_transaction_start(&xbt);
if (err) {
xenbus_dev_fatal(dev, err, "starting transaction");
goto destroy_ring;
}

err = xenbus_printf(xbt, dev->nodename, "tx-ring-ref", "%u",
queue->tx_ring_ref);
if (err) {
message = "writing tx ring-ref";
goto abort_transaction;
}
err = xenbus_printf(xbt, dev->nodename, "rx-ring-ref", "%u",
queue->rx_ring_ref);
if (err) {
message = "writing rx ring-ref";
goto abort_transaction;
}

if (queue->tx_evtchn == queue->rx_evtchn) {
err = xenbus_printf(xbt, dev->nodename,
"event-channel", "%u", queue->tx_evtchn);
if (err) {
message = "writing event-channel";
goto abort_transaction;
}
if (num_queues == 1) {
err = write_queue_xenstore_keys(&info->queues[0], &xbt, 0); /* flat */
if (err)
goto abort_transaction_no_dev_fatal;
} else {
err = xenbus_printf(xbt, dev->nodename,
"event-channel-tx", "%u", queue->tx_evtchn);
/* Write the number of queues */
err = xenbus_printf(xbt, dev->nodename, "multi-queue-num-queues",
"%u", num_queues);
if (err) {
message = "writing event-channel-tx";
goto abort_transaction;
message = "writing multi-queue-num-queues";
goto abort_transaction_no_dev_fatal;
}
err = xenbus_printf(xbt, dev->nodename,
"event-channel-rx", "%u", queue->rx_evtchn);
if (err) {
message = "writing event-channel-rx";
goto abort_transaction;

/* Write the keys for each queue */
for (i = 0; i < num_queues; ++i) {
queue = &info->queues[i];
err = write_queue_xenstore_keys(queue, &xbt, 1); /* hierarchical */
if (err)
goto abort_transaction_no_dev_fatal;
}
}

/* The remaining keys are not queue-specific */
err = xenbus_printf(xbt, dev->nodename, "request-rx-copy", "%u",
1);
if (err) {
Expand Down Expand Up @@ -1857,8 +1951,9 @@ static int talk_to_netback(struct xenbus_device *dev,
return 0;

abort_transaction:
xenbus_transaction_end(xbt, 1);
xenbus_dev_fatal(dev, err, "%s", message);
abort_transaction_no_dev_fatal:
xenbus_transaction_end(xbt, 1);
destroy_ring:
xennet_disconnect_backend(info);
kfree(info->queues);
Expand Down Expand Up @@ -2264,6 +2359,9 @@ static int __init netif_init(void)

pr_info("Initialising Xen virtual ethernet driver\n");

/* Allow as many queues as there are CPUs, by default */
xennet_max_queues = num_online_cpus();

return xenbus_register_frontend(&netfront_driver);
}
module_init(netif_init);
Expand Down

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