[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] [Xen-changelog] [linux-2.6.18-xen] sfc_netfront: Only clear tx_skb when ready for netif_wake_queue
# HG changeset patch # User Keir Fraser <keir.fraser@xxxxxxxxxx> # Date 1238497253 -3600 # Node ID 3a4410c4504ea64f2c1e873df3234938366050ad # Parent ab1d4fbbe4bf93f203e0c4d62c18bd248e4f1d4a sfc_netfront: Only clear tx_skb when ready for netif_wake_queue (doing otherwise could result in a lost packet) and document use of locks to protect tx_skb Signed-off-by: Kieran Mansley <kmansley@xxxxxxxxxxxxxx> --- drivers/xen/sfc_netfront/accel.h | 6 +++-- drivers/xen/sfc_netfront/accel_netfront.c | 4 +-- drivers/xen/sfc_netfront/accel_vi.c | 35 ++++++++++++------------------ 3 files changed, 21 insertions(+), 24 deletions(-) diff -r ab1d4fbbe4bf -r 3a4410c4504e drivers/xen/sfc_netfront/accel.h --- a/drivers/xen/sfc_netfront/accel.h Tue Mar 31 12:00:03 2009 +0100 +++ b/drivers/xen/sfc_netfront/accel.h Tue Mar 31 12:00:53 2009 +0100 @@ -277,8 +277,10 @@ typedef struct netfront_accel_vnic { int poll_enabled; - /** A spare slot for a TX packet. This is treated as an extension - * of the DMA queue. */ + /** A spare slot for a TX packet. This is treated as an + * extension of the DMA queue. Reads require either + * netfront's tx_lock or the vnic tx_lock; writes require both + * locks */ struct sk_buff *tx_skb; /** Keep track of fragments of SSR packets */ diff -r ab1d4fbbe4bf -r 3a4410c4504e drivers/xen/sfc_netfront/accel_netfront.c --- a/drivers/xen/sfc_netfront/accel_netfront.c Tue Mar 31 12:00:03 2009 +0100 +++ b/drivers/xen/sfc_netfront/accel_netfront.c Tue Mar 31 12:00:53 2009 +0100 @@ -65,7 +65,7 @@ static int netfront_accel_netdev_start_x BUG_ON(vnic->net_dev != net_dev); DPRINTK("%s stopping queue\n", __FUNCTION__); - /* Netfront's lock protects tx_skb */ + /* Need netfront's tx_lock and vnic tx_lock to write tx_skb */ spin_lock_irqsave(&np->tx_lock, flags2); BUG_ON(vnic->tx_skb != NULL); vnic->tx_skb = skb; @@ -183,7 +183,7 @@ static int netfront_accel_check_ready(st BUG_ON(vnic == NULL); - /* This is protected by netfront's lock */ + /* Read of tx_skb is protected by netfront's tx_lock */ return vnic->tx_skb == NULL; } diff -r ab1d4fbbe4bf -r 3a4410c4504e drivers/xen/sfc_netfront/accel_vi.c --- a/drivers/xen/sfc_netfront/accel_vi.c Tue Mar 31 12:00:03 2009 +0100 +++ b/drivers/xen/sfc_netfront/accel_vi.c Tue Mar 31 12:00:53 2009 +0100 @@ -991,39 +991,35 @@ static void netfront_accel_vi_not_busy(n { struct netfront_info *np = ((struct netfront_info *) netdev_priv(vnic->net_dev)); - struct sk_buff *skb; int handled; unsigned long flags; - + /* - * TODO if we could safely check tx_skb == NULL and return - * early without taking the lock, that would obviously help - * performance - */ - - /* Take the netfront lock which protects tx_skb. */ - spin_lock_irqsave(&np->tx_lock, flags); + * We hold the vnic tx_lock which is sufficient to exclude + * writes to tx_skb + */ + if (vnic->tx_skb != NULL) { DPRINTK("%s trying to send spare buffer\n", __FUNCTION__); - skb = vnic->tx_skb; - vnic->tx_skb = NULL; - - spin_unlock_irqrestore(&np->tx_lock, flags); - - handled = netfront_accel_vi_tx_post(vnic, skb); + handled = netfront_accel_vi_tx_post(vnic, vnic->tx_skb); - spin_lock_irqsave(&np->tx_lock, flags); - if (handled != NETFRONT_ACCEL_STATUS_BUSY) { DPRINTK("%s restarting tx\n", __FUNCTION__); + + /* Need netfront tx_lock and vnic tx_lock to + * write tx_skb */ + spin_lock_irqsave(&np->tx_lock, flags); + + vnic->tx_skb = NULL; + if (netfront_check_queue_ready(vnic->net_dev)) { netif_wake_queue(vnic->net_dev); NETFRONT_ACCEL_STATS_OP (vnic->stats.queue_wakes++); } - } else { - vnic->tx_skb = skb; + spin_unlock_irqrestore(&np->tx_lock, flags); + } /* @@ -1032,7 +1028,6 @@ static void netfront_accel_vi_not_busy(n */ BUG_ON(handled == NETFRONT_ACCEL_STATUS_CANT); } - spin_unlock_irqrestore(&np->tx_lock, flags); } _______________________________________________ Xen-changelog mailing list Xen-changelog@xxxxxxxxxxxxxxxxxxx http://lists.xensource.com/xen-changelog
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