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Date: Fri, 7 Apr 2017 13:31:00 +1000
From: Benjamin Herrenschmidt <benh@...nel.crashing.org>
To: netdev@...r.kernel.org
Cc: Benjamin Herrenschmidt <benh@...nel.crashing.org>
Subject: [PATCH 07/12] 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 <benh@...nel.crashing.org>
---
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 ff01dfb..ccf0fcd 100644
--- a/drivers/net/ethernet/faraday/ftgmac100.c
+++ b/drivers/net/ethernet/faraday/ftgmac100.c
@@ -44,6 +44,9 @@
#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];
@@ -66,9 +69,7 @@ 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;
@@ -163,7 +164,6 @@ 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))
@@ -549,6 +549,23 @@ 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;
@@ -557,9 +574,6 @@ 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];
@@ -581,18 +595,31 @@ 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,
@@ -651,17 +678,22 @@ 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);
@@ -979,17 +1011,17 @@ 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
@@ -1003,11 +1035,13 @@ 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
@@ -1015,7 +1049,8 @@ 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 */
@@ -1026,7 +1061,7 @@ 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)
@@ -1354,8 +1389,6 @@ 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));
--
2.9.3
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