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Date: Wed, 4 Aug 2010 19:37:23 +0800
From: Changli Gao <xiaosuo@...il.com>
To: Krishna Kumar <krkumar2@...ibm.com>
Cc: davem@...emloft.net, arnd@...db.de, mst@...hat.com,
netdev@...r.kernel.org, bhutchings@...arflare.com,
therbert@...gle.com
Subject: Re: [PATCH v4 2/2] macvtap: Implement multiqueue for macvtap driver
On Wed, Aug 4, 2010 at 6:55 PM, Krishna Kumar <krkumar2@...ibm.com> wrote:
> From: Krishna Kumar <krkumar2@...ibm.com>
>
> Implement multiqueue facility for macvtap driver. The idea is that
> a macvtap device can be opened multiple times and the fd's can be
> used to register eg, as backend for vhost.
>
> Signed-off-by: Krishna Kumar <krkumar2@...ibm.com>
> ---
> drivers/net/macvtap.c | 89 ++++++++++++++++++++++++++++-------
> include/linux/if_macvlan.h | 9 +++
> 2 files changed, 80 insertions(+), 18 deletions(-)
>
> diff -ruNp org/drivers/net/macvtap.c new/drivers/net/macvtap.c
> --- org/drivers/net/macvtap.c 2010-07-28 15:10:10.000000000 +0530
> +++ new/drivers/net/macvtap.c 2010-08-04 16:19:32.000000000 +0530
> @@ -84,26 +84,45 @@ static const struct proto_ops macvtap_so
> static DEFINE_SPINLOCK(macvtap_lock);
>
> /*
> - * Choose the next free queue, for now there is only one
> + * get_slot: return a [unused/occupied] slot in vlan->taps[]:
> + * - if 'q' is NULL, return the first empty slot;
> + * - otherwise, return the slot this pointer occupies.
> */
> +static int get_slot(struct macvlan_dev *vlan, struct macvtap_queue *q)
> +{
> + int i;
> +
> + for (i = 0; i < MAX_MACVTAP_QUEUES; i++) {
> + if (rcu_dereference(vlan->taps[i]) == q)
> + return i;
> + }
> +
> + /* Should never happen */
> + BUG_ON(1);
> +}
> +
> static int macvtap_set_queue(struct net_device *dev, struct file *file,
> struct macvtap_queue *q)
> {
> struct macvlan_dev *vlan = netdev_priv(dev);
> + int index;
> int err = -EBUSY;
>
> spin_lock(&macvtap_lock);
> - if (rcu_dereference(vlan->tap))
> + if (vlan->numvtaps == MAX_MACVTAP_QUEUES)
> goto out;
>
> err = 0;
> + index = get_slot(vlan, NULL);
> rcu_assign_pointer(q->vlan, vlan);
> - rcu_assign_pointer(vlan->tap, q);
> + rcu_assign_pointer(vlan->taps[index], q);
> sock_hold(&q->sk);
>
> q->file = file;
> file->private_data = q;
>
> + vlan->numvtaps++;
> +
> out:
> spin_unlock(&macvtap_lock);
> return err;
> @@ -124,9 +143,12 @@ static void macvtap_put_queue(struct mac
> spin_lock(&macvtap_lock);
> vlan = rcu_dereference(q->vlan);
> if (vlan) {
> - rcu_assign_pointer(vlan->tap, NULL);
> + int index = get_slot(vlan, q);
> +
> + rcu_assign_pointer(vlan->taps[index], NULL);
> rcu_assign_pointer(q->vlan, NULL);
> sock_put(&q->sk);
> + --vlan->numvtaps;
> }
>
> spin_unlock(&macvtap_lock);
> @@ -136,39 +158,72 @@ static void macvtap_put_queue(struct mac
> }
>
> /*
> - * Since we only support one queue, just dereference the pointer.
> + * Select a queue based on the rxq of the device on which this packet
> + * arrived. If the incoming device is not mq, calculate a flow hash to
> + * select a queue. vlan->numvtaps is cached in case it reduces during
> + * the execution of this function.
> */
> static struct macvtap_queue *macvtap_get_queue(struct net_device *dev,
> struct sk_buff *skb)
> {
> struct macvlan_dev *vlan = netdev_priv(dev);
> + struct macvtap_queue *tap = NULL;
> + int numvtaps = vlan->numvtaps;
> + __u32 rxq;
> +
> + if (!numvtaps)
> + goto out;
> +
> + if (likely(skb_rx_queue_recorded(skb))) {
> + rxq = skb_get_rx_queue(skb);
> +
> + while (unlikely(rxq >= numvtaps))
> + rxq -= numvtaps;
>
> - return rcu_dereference(vlan->tap);
> + tap = rcu_dereference(vlan->taps[rxq]);
> + if (tap)
> + goto out;
> + }
> +
> + rxq = skb_get_rxhash(skb);
> + if (!rxq)
> + rxq = smp_processor_id();
> +
> + tap = rcu_dereference(vlan->taps[rxq & (numvtaps - 1)]);
> +
numvtaps maybe not power of 2. So some queue maybe can't be used.
You'd better maintain a online queue map and get the index as
get_rps_cpu() dones.
((u64)rxhash * numvtaps) >> 32
for the sbks, we can't get a valid rxhash, we'd better pass them to a
specified queue, such as queue 0.
> +out:
> + return tap;
> }
>
> /*
> * The net_device is going away, give up the reference
> - * that it holds on the queue (all the queues one day)
> - * and safely set the pointer from the queues to NULL.
> + * that it holds on all queues and safely set the pointer
> + * from the queues to NULL.
> */
> static void macvtap_del_queues(struct net_device *dev)
> {
> struct macvlan_dev *vlan = netdev_priv(dev);
> - struct macvtap_queue *q;
> + struct macvtap_queue *q, *qlist[MAX_MACVTAP_QUEUES];
> + int i, j = 0;
>
> + /* macvtap_put_queue can free some slots, so go through all slots */
> spin_lock(&macvtap_lock);
> - q = rcu_dereference(vlan->tap);
> - if (!q) {
> - spin_unlock(&macvtap_lock);
> - return;
> + for (i = 0; i < MAX_MACVTAP_QUEUES && vlan->numvtaps; i++) {
> + q = rcu_dereference(vlan->taps[i]);
> + if (q) {
> + qlist[j++] = q;
> + rcu_assign_pointer(vlan->taps[i], NULL);
> + rcu_assign_pointer(q->vlan, NULL);
> + vlan->numvtaps--;
> + }
> }
> -
> - rcu_assign_pointer(vlan->tap, NULL);
> - rcu_assign_pointer(q->vlan, NULL);
> + BUG_ON(vlan->numvtaps != 0);
> spin_unlock(&macvtap_lock);
>
> synchronize_rcu();
> - sock_put(&q->sk);
> +
> + for (--j; j >= 0; j--)
> + sock_put(&qlist[j]->sk);
> }
>
> /*
> diff -ruNp org/include/linux/if_macvlan.h new/include/linux/if_macvlan.h
> --- org/include/linux/if_macvlan.h 2010-07-28 15:10:10.000000000 +0530
> +++ new/include/linux/if_macvlan.h 2010-08-04 16:19:32.000000000 +0530
> @@ -40,6 +40,12 @@ struct macvlan_rx_stats {
> unsigned long rx_errors;
> };
>
> +/*
> + * Maximum times a macvtap device can be opened. This can be used to
> + * configure the number of receive queue, e.g. for multiqueue virtio.
> + */
> +#define MAX_MACVTAP_QUEUES (NR_CPUS < 16 ? NR_CPUS : 16)
> +
> struct macvlan_dev {
> struct net_device *dev;
> struct list_head list;
> @@ -50,7 +56,8 @@ struct macvlan_dev {
> enum macvlan_mode mode;
> int (*receive)(struct sk_buff *skb);
> int (*forward)(struct net_device *dev, struct sk_buff *skb);
> - struct macvtap_queue *tap;
> + struct macvtap_queue *taps[MAX_MACVTAP_QUEUES];
> + int numvtaps;
> };
>
> static inline void macvlan_count_rx(const struct macvlan_dev *vlan,
>
--
Regards,
Changli Gao(xiaosuo@...il.com)
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