From 6ad3d7edcbdae233a24f67a6713f461b2325e5cc Mon Sep 17 00:00:00 2001 From: Benjamin Herrenschmidt Date: Mon, 10 Apr 2017 11:15:21 +1000 Subject: [PATCH] ftgmac100: Cleanup tx queue handling We have a private lock which isn't terribly useful, and we maintain a "tx_pending" counter for information that's already available via a trivial arithmetic operation. Then we unconditionaly wake the queue even when not stopped. Finally our code in tx isn't really safe vs. a concurrent reclaim. The aspeed chips aren't SMP today but I prefer the code being right and future proof. So rip that out and replace it with more "standard" queue handling, currently with a threshold of 1 queue element, which will be increased when we implement fragmented sends. Signed-off-by: Benjamin Herrenschmidt Signed-off-by: David S. Miller --- drivers/net/ethernet/faraday/ftgmac100.c | 103 +++++++++++++++-------- 1 file changed, 68 insertions(+), 35 deletions(-) diff --git a/drivers/net/ethernet/faraday/ftgmac100.c b/drivers/net/ethernet/faraday/ftgmac100.c index b4d84e753187..add7462bf67d 100644 --- a/drivers/net/ethernet/faraday/ftgmac100.c +++ b/drivers/net/ethernet/faraday/ftgmac100.c @@ -46,6 +46,9 @@ #define MAX_PKT_SIZE 1536 #define RX_BUF_SIZE MAX_PKT_SIZE /* must be smaller than 0x3fff */ +/* Min number of tx ring entries before stopping queue */ +#define TX_THRESHOLD (1) + struct ftgmac100_descs { struct ftgmac100_rxdes rxdes[RX_QUEUE_ENTRIES]; struct ftgmac100_txdes txdes[TX_QUEUE_ENTRIES]; @@ -68,9 +71,7 @@ struct ftgmac100 { struct sk_buff *tx_skbs[TX_QUEUE_ENTRIES]; unsigned int tx_clean_pointer; unsigned int tx_pointer; - unsigned int tx_pending; u32 txdes0_edotr_mask; - spinlock_t tx_lock; /* Scratch page to use when rx skb alloc fails */ void *rx_scratch; @@ -165,7 +166,6 @@ static int ftgmac100_reset_and_config_mac(struct ftgmac100 *priv) priv->rx_pointer = 0; priv->tx_clean_pointer = 0; priv->tx_pointer = 0; - priv->tx_pending = 0; /* The doc says reset twice with 10us interval */ if (ftgmac100_reset_mac(priv, maccr)) @@ -551,6 +551,23 @@ static int ftgmac100_next_tx_pointer(int pointer) return (pointer + 1) & (TX_QUEUE_ENTRIES - 1); } +static u32 ftgmac100_tx_buf_avail(struct ftgmac100 *priv) +{ + /* Returns the number of available slots in the TX queue + * + * This always leaves one free slot so we don't have to + * worry about empty vs. full, and this simplifies the + * test for ftgmac100_tx_buf_cleanable() below + */ + return (priv->tx_clean_pointer - priv->tx_pointer - 1) & + (TX_QUEUE_ENTRIES - 1); +} + +static bool ftgmac100_tx_buf_cleanable(struct ftgmac100 *priv) +{ + return priv->tx_pointer != priv->tx_clean_pointer; +} + static bool ftgmac100_tx_complete_packet(struct ftgmac100 *priv) { struct net_device *netdev = priv->netdev; @@ -559,9 +576,6 @@ static bool ftgmac100_tx_complete_packet(struct ftgmac100 *priv) struct sk_buff *skb; dma_addr_t map; - if (priv->tx_pending == 0) - return false; - pointer = priv->tx_clean_pointer; txdes = &priv->descs->txdes[pointer]; @@ -583,18 +597,31 @@ static bool ftgmac100_tx_complete_packet(struct ftgmac100 *priv) priv->tx_clean_pointer = ftgmac100_next_tx_pointer(pointer); - spin_lock(&priv->tx_lock); - priv->tx_pending--; - spin_unlock(&priv->tx_lock); - netif_wake_queue(netdev); - return true; } static void ftgmac100_tx_complete(struct ftgmac100 *priv) { - while (ftgmac100_tx_complete_packet(priv)) + struct net_device *netdev = priv->netdev; + + /* Process all completed packets */ + while (ftgmac100_tx_buf_cleanable(priv) && + ftgmac100_tx_complete_packet(priv)) ; + + /* Restart queue if needed */ + smp_mb(); + if (unlikely(netif_queue_stopped(netdev) && + ftgmac100_tx_buf_avail(priv) >= TX_THRESHOLD)) { + struct netdev_queue *txq; + + txq = netdev_get_tx_queue(netdev, 0); + __netif_tx_lock(txq, smp_processor_id()); + if (netif_queue_stopped(netdev) && + ftgmac100_tx_buf_avail(priv) >= TX_THRESHOLD) + netif_wake_queue(netdev); + __netif_tx_unlock(txq); + } } static int ftgmac100_hard_start_xmit(struct sk_buff *skb, @@ -652,17 +679,22 @@ static int ftgmac100_hard_start_xmit(struct sk_buff *skb, } } + ftgmac100_txdes_set_dma_own(txdes); + /* Update next TX pointer */ priv->tx_pointer = ftgmac100_next_tx_pointer(pointer); - spin_lock(&priv->tx_lock); - priv->tx_pending++; - if (priv->tx_pending == TX_QUEUE_ENTRIES) + /* If there isn't enough room for all the fragments of a new packet + * in the TX ring, stop the queue. The sequence below is race free + * vs. a concurrent restart in ftgmac100_poll() + */ + if (unlikely(ftgmac100_tx_buf_avail(priv) < TX_THRESHOLD)) { netif_stop_queue(netdev); - - /* start transmit */ - ftgmac100_txdes_set_dma_own(txdes); - spin_unlock(&priv->tx_lock); + /* Order the queue stop with the test below */ + smp_mb(); + if (ftgmac100_tx_buf_avail(priv) >= TX_THRESHOLD) + netif_wake_queue(netdev); + } ftgmac100_txdma_normal_prio_start_polling(priv); @@ -980,17 +1012,17 @@ static bool ftgmac100_check_rx(struct ftgmac100 *priv) static int ftgmac100_poll(struct napi_struct *napi, int budget) { struct ftgmac100 *priv = container_of(napi, struct ftgmac100, napi); - bool more, completed = true; - int rx = 0; + int work_done = 0; + bool more; - ftgmac100_tx_complete(priv); + /* Handle TX completions */ + if (ftgmac100_tx_buf_cleanable(priv)) + ftgmac100_tx_complete(priv); + /* Handle RX packets */ do { - more = ftgmac100_rx_packet(priv, &rx); - } while (more && rx < budget); - - if (more && rx == budget) - completed = false; + more = ftgmac100_rx_packet(priv, &work_done); + } while (more && work_done < budget); /* The interrupt is telling us to kick the MAC back to life @@ -1004,11 +1036,13 @@ static int ftgmac100_poll(struct napi_struct *napi, int budget) priv->base + FTGMAC100_OFFSET_IER); } - /* Keep NAPI going if we have still packets to reclaim */ - if (priv->tx_pending) - return budget; + /* As long as we are waiting for transmit packets to be + * completed we keep NAPI going + */ + if (ftgmac100_tx_buf_cleanable(priv)) + work_done = budget; - if (completed) { + if (work_done < budget) { /* We are about to re-enable all interrupts. However * the HW has been latching RX/TX packet interrupts while * they were masked. So we clear them first, then we need @@ -1016,7 +1050,8 @@ static int ftgmac100_poll(struct napi_struct *napi, int budget) */ iowrite32(FTGMAC100_INT_RXTX, priv->base + FTGMAC100_OFFSET_ISR); - if (ftgmac100_check_rx(priv) || priv->tx_pending) + if (ftgmac100_check_rx(priv) || + ftgmac100_tx_buf_cleanable(priv)) return budget; /* deschedule NAPI */ @@ -1027,7 +1062,7 @@ static int ftgmac100_poll(struct napi_struct *napi, int budget) priv->base + FTGMAC100_OFFSET_IER); } - return rx; + return work_done; } static int ftgmac100_init_all(struct ftgmac100 *priv, bool ignore_alloc_err) @@ -1355,8 +1390,6 @@ static int ftgmac100_probe(struct platform_device *pdev) priv->dev = &pdev->dev; INIT_WORK(&priv->reset_task, ftgmac100_reset_task); - spin_lock_init(&priv->tx_lock); - /* map io memory */ priv->res = request_mem_region(res->start, resource_size(res), dev_name(&pdev->dev)); -- 2.20.1