Re: [Xen-devel] [PATCH V4 net-next 2/5] xen-netback: Add support for multiple queues

[Andrew Bennieston <andrew.bennieston@xxxxxxxxxx>]

On 21/02/14 12:13, Paul Durrant wrote:
> > -----Original Message-----
> > From: Andrew J. Bennieston [mailto:andrew.bennieston@xxxxxxxxxx]
> > Sent: 17 February 2014 17:58
> > To: xen-devel@xxxxxxxxxxxxxxxxxxxx
> > Cc: Ian Campbell; Wei Liu; Paul Durrant; netdev@xxxxxxxxxxxxxxx; David
> > Vrabel; Andrew Bennieston
> > Subject: [PATCH V4 net-next 2/5] xen-netback: Add support for multiple
> > queues
> >
> > From: "Andrew J. Bennieston" <andrew.bennieston@xxxxxxxxxx>
> >
> > Builds on the refactoring of the previous patch to implement multiple
> > queues between xen-netfront and xen-netback.
> >
> > Writes the maximum supported number of queues into XenStore, and reads
> > the values written by the frontend to determine how many queues to use.
> >
> > Ring references and event channels are read from XenStore on a per-queue
> > basis and rings are connected accordingly.
> >
> > Signed-off-by: Andrew J. Bennieston <andrew.bennieston@xxxxxxxxxx>
> > ---
> >   drivers/net/xen-netback/common.h    |    2 +
> >   drivers/net/xen-netback/interface.c |    7 +++-
> >   drivers/net/xen-netback/netback.c   |    8 ++++
> >   drivers/net/xen-netback/xenbus.c    |   76
> > ++++++++++++++++++++++++++++++-----
> >   4 files changed, 82 insertions(+), 11 deletions(-)
> >
> > diff --git a/drivers/net/xen-netback/common.h b/drivers/net/xen-
> > netback/common.h
> > index 2550867..8180929 100644
> > --- a/drivers/net/xen-netback/common.h
> > +++ b/drivers/net/xen-netback/common.h
> > @@ -261,4 +261,6 @@ void xenvif_carrier_on(struct xenvif *vif);
> >
> >   extern bool separate_tx_rx_irq;
> >
> > +extern unsigned int xenvif_max_queues;
> > +
> >   #endif /* __XEN_NETBACK__COMMON_H__ */
> > diff --git a/drivers/net/xen-netback/interface.c b/drivers/net/xen-
> > netback/interface.c
> > index daf93f6..bc7a82d 100644
> > --- a/drivers/net/xen-netback/interface.c
> > +++ b/drivers/net/xen-netback/interface.c
> > @@ -373,7 +373,12 @@ struct xenvif *xenvif_alloc(struct device *parent,
> > domid_t domid,
> >         char name[IFNAMSIZ] = {};
> >
> >         snprintf(name, IFNAMSIZ - 1, "vif%u.%u", domid, handle);
> > -       dev = alloc_netdev_mq(sizeof(struct xenvif), name, ether_setup, 1);
> > +       /* Allocate a netdev with the max. supported number of queues.
> > +        * When the guest selects the desired number, it will be updated
> > +        * via netif_set_real_num_tx_queues().
> > +        */
> > +       dev = alloc_netdev_mq(sizeof(struct xenvif), name, ether_setup,
> > +                             xenvif_max_queues);
> >         if (dev == NULL) {
> >                 pr_warn("Could not allocate netdev for %s\n", name);
> >                 return ERR_PTR(-ENOMEM);
> > diff --git a/drivers/net/xen-netback/netback.c b/drivers/net/xen-
> > netback/netback.c
> > index 46b2f5b..64d66a1 100644
> > --- a/drivers/net/xen-netback/netback.c
> > +++ b/drivers/net/xen-netback/netback.c
> > @@ -54,6 +54,11 @@
> >   bool separate_tx_rx_irq = 1;
> >   module_param(separate_tx_rx_irq, bool, 0644);
> >
> > +unsigned int xenvif_max_queues;
> > +module_param(xenvif_max_queues, uint, 0644);
> > +MODULE_PARM_DESC(xenvif_max_queues,
> > +               "Maximum number of queues per virtual interface");
> > +
> >   /*
> >    * This is the maximum slots a skb can have. If a guest sends a skb
> >    * which exceeds this limit it is considered malicious.
> > @@ -1585,6 +1590,9 @@ static int __init netback_init(void)
> >         if (!xen_domain())
> >                 return -ENODEV;
> >
> > +       /* Allow as many queues as there are CPUs, by default */
> > +       xenvif_max_queues = num_online_cpus();
> > +
> >         if (fatal_skb_slots < XEN_NETBK_LEGACY_SLOTS_MAX) {
> >                 pr_info("fatal_skb_slots too small (%d), bump it to
> > XEN_NETBK_LEGACY_SLOTS_MAX (%d)\n",
> >                         fatal_skb_slots, XEN_NETBK_LEGACY_SLOTS_MAX);
> > diff --git a/drivers/net/xen-netback/xenbus.c b/drivers/net/xen-
> > netback/xenbus.c
> > index f23ea0a..d11f51e 100644
> > --- a/drivers/net/xen-netback/xenbus.c
> > +++ b/drivers/net/xen-netback/xenbus.c
> > @@ -20,6 +20,7 @@
> >
> >   #include "common.h"
> >   #include <linux/vmalloc.h>
> > +#include <linux/rtnetlink.h>
> >
> >   struct backend_info {
> >         struct xenbus_device *dev;
> > @@ -159,6 +160,12 @@ static int netback_probe(struct xenbus_device *dev,
> >         if (err)
> >                 pr_debug("Error writing feature-split-event-channels\n");
> >
> > +       /* Multi-queue support: This is an optional feature. */
> > +       err = xenbus_printf(XBT_NIL, dev->nodename,
> > +                       "multi-queue-max-queues", "%u",
> > xenvif_max_queues);
> > +       if (err)
> > +               pr_debug("Error writing multi-queue-max-queues\n");
> > +
> >         err = xenbus_switch_state(dev, XenbusStateInitWait);
> >         if (err)
> >                 goto fail;
> > @@ -490,6 +497,23 @@ static void connect(struct backend_info *be)
> >         unsigned long credit_bytes, credit_usec;
> >         unsigned int queue_index;
> >         struct xenvif_queue *queue;
> > +       unsigned int requested_num_queues;
> > +
> > +       /* Check whether the frontend requested multiple queues
> > +        * and read the number requested.
> > +        */
> > +       err = xenbus_scanf(XBT_NIL, dev->otherend,
> > +                       "multi-queue-num-queues",
> > +                       "%u", &requested_num_queues);
> > +       if (err < 0) {
> > +               requested_num_queues = 1; /* Fall back to single queue */
> > +       } else if (requested_num_queues > xenvif_max_queues) {
> > +               /* buggy or malicious guest */
> > +               xenbus_dev_fatal(dev, err,
> > +                       "guest requested %u queues, exceeding the
> > maximum of %u.",
> > +                       requested_num_queues, xenvif_max_queues);
> > +               return;
> > +       }
> >
> >         err = xen_net_read_mac(dev, be->vif->fe_dev_addr);
> >         if (err) {
> > @@ -500,9 +524,13 @@ static void connect(struct backend_info *be)
> >         xen_net_read_rate(dev, &credit_bytes, &credit_usec);
> >         read_xenbus_vif_flags(be);
> >
> > -       be->vif->num_queues = 1;
> > +       /* Use the number of queues requested by the frontend */
> > +       be->vif->num_queues = requested_num_queues;
> >         be->vif->queues = vzalloc(be->vif->num_queues *
> >                         sizeof(struct xenvif_queue));
> > +       rtnl_lock();
> > +       netif_set_real_num_tx_queues(be->vif->dev, be->vif-
> > > num_queues);
> > +       rtnl_unlock();
> >
> >         for (queue_index = 0; queue_index < be->vif->num_queues;
> > ++queue_index) {
> >                 queue = &be->vif->queues[queue_index];
> > @@ -547,29 +575,52 @@ static int connect_rings(struct backend_info *be,
> > struct xenvif_queue *queue)
> >         unsigned long tx_ring_ref, rx_ring_ref;
> >         unsigned int tx_evtchn, rx_evtchn;
> >         int err;
> > +       char *xspath = NULL;
> I don't think you need the NULL init here. xspath is set in both branches of 
> the if statement below.
Indeed, but I prefer to initialise things sanely where possible. It 
makes it easier to spot problems with later modifications of the code, 
e.g. if one of those branches changed.
Andrew.
>    Paul
>
> > +       size_t xspathsize;
> > +       const size_t xenstore_path_ext_size = 11; /* sufficient for "/queue-
> > NNN" */
> > +
> > +       /* If the frontend requested 1 queue, or we have fallen back
> > +        * to single queue due to lack of frontend support for multi-
> > +        * queue, expect the remaining XenStore keys in the toplevel
> > +        * directory. Otherwise, expect them in a subdirectory called
> > +        * queue-N.
> > +        */
> > +       if (queue->vif->num_queues == 1) {
> > +               xspath = (char *)dev->otherend;
> > +       } else {
> > +               xspathsize = strlen(dev->otherend) +
> > xenstore_path_ext_size;
> > +               xspath = kzalloc(xspathsize, GFP_KERNEL);
> > +               if (!xspath) {
> > +                       xenbus_dev_fatal(dev, -ENOMEM,
> > +                                       "reading ring references");
> > +                       return -ENOMEM;
> > +               }
> > +               snprintf(xspath, xspathsize, "%s/queue-%u", dev-
> > > otherend,
> > +                                queue->id);
> > +       }
> >
> > -       err = xenbus_gather(XBT_NIL, dev->otherend,
> > +       err = xenbus_gather(XBT_NIL, xspath,
> >                             "tx-ring-ref", "%lu", &tx_ring_ref,
> >                             "rx-ring-ref", "%lu", &rx_ring_ref, NULL);
> >         if (err) {
> >                 xenbus_dev_fatal(dev, err,
> >                                  "reading %s/ring-ref",
> > -                                dev->otherend);
> > -               return err;
> > +                                xspath);
> > +               goto err;
> >         }
> >
> >         /* Try split event channels first, then single event channel. */
> > -       err = xenbus_gather(XBT_NIL, dev->otherend,
> > +       err = xenbus_gather(XBT_NIL, xspath,
> >                             "event-channel-tx", "%u", &tx_evtchn,
> >                             "event-channel-rx", "%u", &rx_evtchn, NULL);
> >         if (err < 0) {
> > -               err = xenbus_scanf(XBT_NIL, dev->otherend,
> > +               err = xenbus_scanf(XBT_NIL, xspath,
> >                                    "event-channel", "%u", &tx_evtchn);
> >                 if (err < 0) {
> >                         xenbus_dev_fatal(dev, err,
> >                                          "reading %s/event-channel(-tx/rx)",
> > -                                        dev->otherend);
> > -                       return err;
> > +                                        xspath);
> > +                       goto err;
> >                 }
> >                 rx_evtchn = tx_evtchn;
> >         }
> > @@ -582,10 +633,15 @@ static int connect_rings(struct backend_info *be,
> > struct xenvif_queue *queue)
> >                                  "mapping shared-frames %lu/%lu port tx %u
> > rx %u",
> >                                  tx_ring_ref, rx_ring_ref,
> >                                  tx_evtchn, rx_evtchn);
> > -               return err;
> > +               goto err;
> >         }
> >
> > -       return 0;
> > +       err = 0;
> > +err: /* Regular return falls through with err == 0 */
> > +       if (xspath != dev->otherend)
> > +               kfree(xspath);
> > +
> > +       return err;
> >   }
> >
> >   static int read_xenbus_vif_flags(struct backend_info *be)
> > --
> > 1.7.10.4

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