From patchwork Fri Sep 21 09:11:15 2012 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Subject: [v3] ucc_geth: Lockless xmit Date: Thu, 20 Sep 2012 23:11:15 -0000 From: Joakim Tjernlund X-Patchwork-Id: 185631 Message-Id: <1348218675-3804-1-git-send-email-Joakim.Tjernlund@transmode.se> To: Francois Romieu , netdev@vger.kernel.org Cc: Joakim Tjernlund Currently ucc_geth_start_xmit wraps IRQ off for the whole body just to be safe. By rearranging the code a bit one can avoid the lock completely. Signed-off-by: Joakim Tjernlund --- v2: Move assignment of ugeth->tx_skbuff[txQ][ugeth->skb_curtx[txQ]] inside IRQ off section to prevent racing against ucc_geth_tx(). Spotted by Francois Romieu v3: Lockless xmit Here is my attemept to do lockless xmit. Thanks to Francois Romieu for the idea. drivers/net/ethernet/freescale/ucc_geth.c | 17 ++++++++--------- 1 files changed, 8 insertions(+), 9 deletions(-) diff --git a/drivers/net/ethernet/freescale/ucc_geth.c b/drivers/net/ethernet/freescale/ucc_geth.c index 9ac14f8..040aa70 100644 --- a/drivers/net/ethernet/freescale/ucc_geth.c +++ b/drivers/net/ethernet/freescale/ucc_geth.c @@ -3177,19 +3177,20 @@ static int ucc_geth_start_xmit(struct sk_buff *skb, struct net_device *dev) u8 __iomem *bd; /* BD pointer */ u32 bd_status; u8 txQ = 0; - unsigned long flags; ugeth_vdbg("%s: IN", __func__); - spin_lock_irqsave(&ugeth->lock, flags); - dev->stats.tx_bytes += skb->len; + /* We are running in BH disabled context with netif_tx_lock + * and TX reclaim runs via tp->napi.poll inside of a software + * interrupt. Furthermore, IRQ processing runs lockless so we have + * no IRQ context deadlocks to worry about either. Rejoice! + */ + /* Start from the next BD that should be filled */ bd = ugeth->txBd[txQ]; bd_status = in_be32((u32 __iomem *)bd); - /* Save the skb pointer so we can free it later */ - ugeth->tx_skbuff[txQ][ugeth->skb_curtx[txQ]] = skb; /* Update the current skb pointer (wrapping if this was the last) */ ugeth->skb_curtx[txQ] = @@ -3207,6 +3208,8 @@ static int ucc_geth_start_xmit(struct sk_buff *skb, struct net_device *dev) /* set bd status and length */ out_be32((u32 __iomem *)bd, bd_status); + /* Save the skb pointer so we can free it later */ + ugeth->tx_skbuff[txQ][ugeth->skb_curtx[txQ]] = skb; /* Move to next BD in the ring */ if (!(bd_status & T_W)) @@ -3238,8 +3241,6 @@ static int ucc_geth_start_xmit(struct sk_buff *skb, struct net_device *dev) uccf = ugeth->uccf; out_be16(uccf->p_utodr, UCC_FAST_TOD); #endif - spin_unlock_irqrestore(&ugeth->lock, flags); - return NETDEV_TX_OK; } @@ -3387,10 +3388,8 @@ static int ucc_geth_poll(struct napi_struct *napi, int budget) ug_info = ugeth->ug_info; /* Tx event processing */ - spin_lock(&ugeth->lock); for (i = 0; i < ug_info->numQueuesTx; i++) ucc_geth_tx(ugeth->ndev, i); - spin_unlock(&ugeth->lock); howmany = 0; for (i = 0; i < ug_info->numQueuesRx; i++)