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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] [Xen-devel] [PATCH RFC V2] xen-netback: remove guest RX path dependence on MAX_SKB_FRAGS
This dependence is undesirable and logically incorrect.
It's undesirable because Xen network protocol should not depend on a
OS-specific constant.
It's incorrect because the ring slots required doesn't correspond to the
number of frags a SKB has (consider compound page frags).
This patch removes this dependence by correctly counting the ring slots
required.
Change in V2:
Don't play with rx_req_cons_peek, just store the number of slots in
vif->packet_slots.
Only calculate number of ring slots once and store it in SKB control
block for later use.
Signed-off-by: Wei Liu <wei.liu2@xxxxxxxxxx>
---
drivers/net/xen-netback/common.h | 7 ++++++
drivers/net/xen-netback/interface.c | 33 ++++++++++++++++++++++++----
drivers/net/xen-netback/netback.c | 41 ++++++++++++-----------------------
3 files changed, 50 insertions(+), 31 deletions(-)
diff --git a/drivers/net/xen-netback/common.h b/drivers/net/xen-netback/common.h
index 8a4d77e..305b40c 100644
--- a/drivers/net/xen-netback/common.h
+++ b/drivers/net/xen-netback/common.h
@@ -86,6 +86,8 @@ struct xenvif {
* once all queued skbs are put on the ring.
*/
RING_IDX rx_req_cons_peek;
+#define XEN_NETBK_MIN_PACKET_SLOT 1 /* packet must occupy at least 1 slot */
+ unsigned int packet_slots;
/* Transmit shaping: allow 'credit_bytes' every 'credit_usec'. */
unsigned long credit_bytes;
@@ -104,6 +106,11 @@ struct xenvif {
wait_queue_head_t waiting_to_free;
};
+struct skb_cb_overlay {
+ int meta_slots_used;
+ int slots_required;
+};
+
static inline struct xenbus_device *xenvif_to_xenbus_device(struct xenvif *vif)
{
return to_xenbus_device(vif->dev->dev.parent);
diff --git a/drivers/net/xen-netback/interface.c
b/drivers/net/xen-netback/interface.c
index 087d2db..b6393ce 100644
--- a/drivers/net/xen-netback/interface.c
+++ b/drivers/net/xen-netback/interface.c
@@ -96,20 +96,45 @@ static irqreturn_t xenvif_interrupt(int irq, void *dev_id)
static int xenvif_start_xmit(struct sk_buff *skb, struct net_device *dev)
{
struct xenvif *vif = netdev_priv(dev);
+ struct skb_cb_overlay *sco = (struct skb_cb_overlay *)skb->cb;
+ unsigned int ring_slots_required;
BUG_ON(skb->dev != dev);
if (vif->netbk == NULL)
goto drop;
- /* Drop the packet if the target domain has no receive buffers. */
- if (!xenvif_rx_schedulable(vif))
+ ring_slots_required = xen_netbk_count_skb_slots(vif, skb);
+ sco->slots_required = ring_slots_required;
+
+ /* vif->packet_slots stores the ring slots required by
+ * the SKB. The will affect xen_netbk_rx_ring_full. After we
+ * determine what to do with this packet (either queue it or
+ * drop it), packet_slots should be reset to
+ * XEN_NETBK_MIN_PACKET_SLOT (1).
+ */
+ vif->packet_slots = ring_slots_required;
+
+ /* Drop the packet if the target domain has no receive
+ * buffers. This check must go *after* setting
+ * vif->packet_slots as xenvif_rx_schedulable calls
+ * xen_netbk_rx_ring_full.
+ */
+ if (!xenvif_rx_schedulable(vif)) {
+ vif->packet_slots = XEN_NETBK_MIN_PACKET_SLOT;
goto drop;
+ }
- /* Reserve ring slots for the worst-case number of fragments. */
- vif->rx_req_cons_peek += xen_netbk_count_skb_slots(vif, skb);
+ /* Reserve ring slots for the fragments. */
+ vif->rx_req_cons_peek += ring_slots_required;
xenvif_get(vif);
+ /* Resetting packet_slots must go *before*
+ * xen_netbk_must_stop_queue as it calls
+ * xen_netbk_rx_ring_full.
+ */
+ vif->packet_slots = XEN_NETBK_MIN_PACKET_SLOT;
+
if (vif->can_queue && xen_netbk_must_stop_queue(vif))
netif_stop_queue(dev);
diff --git a/drivers/net/xen-netback/netback.c
b/drivers/net/xen-netback/netback.c
index 64828de..2b9f1f3 100644
--- a/drivers/net/xen-netback/netback.c
+++ b/drivers/net/xen-netback/netback.c
@@ -289,21 +289,10 @@ static void xen_netbk_kick_thread(struct xen_netbk *netbk)
wake_up(&netbk->wq);
}
-static int max_required_rx_slots(struct xenvif *vif)
-{
- int max = DIV_ROUND_UP(vif->dev->mtu, PAGE_SIZE);
-
- /* XXX FIXME: RX path dependent on MAX_SKB_FRAGS */
- if (vif->can_sg || vif->gso || vif->gso_prefix)
- max += MAX_SKB_FRAGS + 1; /* extra_info + frags */
-
- return max;
-}
-
int xen_netbk_rx_ring_full(struct xenvif *vif)
{
RING_IDX peek = vif->rx_req_cons_peek;
- RING_IDX needed = max_required_rx_slots(vif);
+ RING_IDX needed = vif->packet_slots;
return ((vif->rx.sring->req_prod - peek) < needed) ||
((vif->rx.rsp_prod_pvt + XEN_NETIF_RX_RING_SIZE - peek) <
needed);
@@ -314,8 +303,7 @@ int xen_netbk_must_stop_queue(struct xenvif *vif)
if (!xen_netbk_rx_ring_full(vif))
return 0;
- vif->rx.sring->req_event = vif->rx_req_cons_peek +
- max_required_rx_slots(vif);
+ vif->rx.sring->req_event = vif->rx_req_cons_peek + vif->packet_slots;
mb(); /* request notification /then/ check the queue */
return xen_netbk_rx_ring_full(vif);
@@ -661,10 +649,6 @@ static void netbk_add_frag_responses(struct xenvif *vif,
int status,
}
}
-struct skb_cb_overlay {
- int meta_slots_used;
-};
-
static void xen_netbk_rx_action(struct xen_netbk *netbk)
{
struct xenvif *vif = NULL, *tmp;
@@ -675,7 +659,6 @@ static void xen_netbk_rx_action(struct xen_netbk *netbk)
struct sk_buff *skb;
LIST_HEAD(notify);
int ret;
- int nr_frags;
int count;
unsigned long offset;
struct skb_cb_overlay *sco;
@@ -690,20 +673,23 @@ static void xen_netbk_rx_action(struct xen_netbk *netbk)
count = 0;
while ((skb = skb_dequeue(&netbk->rx_queue)) != NULL) {
+ unsigned int ring_slots_required;
vif = netdev_priv(skb->dev);
- nr_frags = skb_shinfo(skb)->nr_frags;
sco = (struct skb_cb_overlay *)skb->cb;
- sco->meta_slots_used = netbk_gop_skb(skb, &npo);
- count += nr_frags + 1;
+ ring_slots_required = sco->slots_required;
- __skb_queue_tail(&rxq, skb);
-
- /* Filled the batch queue? */
- /* XXX FIXME: RX path dependent on MAX_SKB_FRAGS */
- if (count + MAX_SKB_FRAGS >= XEN_NETIF_RX_RING_SIZE)
+ if (count + ring_slots_required > XEN_NETIF_RX_RING_SIZE) {
+ skb_queue_head(&netbk->rx_queue, skb);
break;
+ }
+
+ count += ring_slots_required;
+
+ sco->meta_slots_used = netbk_gop_skb(skb, &npo);
+
+ __skb_queue_tail(&rxq, skb);
}
BUG_ON(npo.meta_prod > ARRAY_SIZE(netbk->meta));
@@ -1872,6 +1858,7 @@ int xen_netbk_map_frontend_rings(struct xenvif *vif,
BACK_RING_INIT(&vif->rx, rxs, PAGE_SIZE);
vif->rx_req_cons_peek = 0;
+ vif->packet_slots = XEN_NETBK_MIN_PACKET_SLOT;
return 0;
--
1.7.10.4
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