sfc: Stop TX queues before they fill up
We now have a definite upper bound on the number of descriptors per
skb; use that to stop the queue when the next packet might not fit.
Signed-off-by: Ben Hutchings <bhutchings@solarflare.com>
diff --git a/drivers/net/ethernet/sfc/tx.c b/drivers/net/ethernet/sfc/tx.c
index 24c82f3..330d911 100644
--- a/drivers/net/ethernet/sfc/tx.c
+++ b/drivers/net/ethernet/sfc/tx.c
@@ -22,14 +22,6 @@
#include "nic.h"
#include "workarounds.h"
-/*
- * TX descriptor ring full threshold
- *
- * The tx_queue descriptor ring fill-level must fall below this value
- * before we restart the netif queue
- */
-#define EFX_TXQ_THRESHOLD(_efx) ((_efx)->txq_entries / 2u)
-
static void efx_dequeue_buffer(struct efx_tx_queue *tx_queue,
struct efx_tx_buffer *buffer,
unsigned int *pkts_compl,
@@ -138,6 +130,56 @@
return max_descs;
}
+/* Get partner of a TX queue, seen as part of the same net core queue */
+static struct efx_tx_queue *efx_tx_queue_partner(struct efx_tx_queue *tx_queue)
+{
+ if (tx_queue->queue & EFX_TXQ_TYPE_OFFLOAD)
+ return tx_queue - EFX_TXQ_TYPE_OFFLOAD;
+ else
+ return tx_queue + EFX_TXQ_TYPE_OFFLOAD;
+}
+
+static void efx_tx_maybe_stop_queue(struct efx_tx_queue *txq1)
+{
+ /* We need to consider both queues that the net core sees as one */
+ struct efx_tx_queue *txq2 = efx_tx_queue_partner(txq1);
+ struct efx_nic *efx = txq1->efx;
+ unsigned int fill_level;
+
+ fill_level = max(txq1->insert_count - txq1->old_read_count,
+ txq2->insert_count - txq2->old_read_count);
+ if (likely(fill_level < efx->txq_stop_thresh))
+ return;
+
+ /* We used the stale old_read_count above, which gives us a
+ * pessimistic estimate of the fill level (which may even
+ * validly be >= efx->txq_entries). Now try again using
+ * read_count (more likely to be a cache miss).
+ *
+ * If we read read_count and then conditionally stop the
+ * queue, it is possible for the completion path to race with
+ * us and complete all outstanding descriptors in the middle,
+ * after which there will be no more completions to wake it.
+ * Therefore we stop the queue first, then read read_count
+ * (with a memory barrier to ensure the ordering), then
+ * restart the queue if the fill level turns out to be low
+ * enough.
+ */
+ netif_tx_stop_queue(txq1->core_txq);
+ smp_mb();
+ txq1->old_read_count = ACCESS_ONCE(txq1->read_count);
+ txq2->old_read_count = ACCESS_ONCE(txq2->read_count);
+
+ fill_level = max(txq1->insert_count - txq1->old_read_count,
+ txq2->insert_count - txq2->old_read_count);
+ EFX_BUG_ON_PARANOID(fill_level >= efx->txq_entries);
+ if (likely(fill_level < efx->txq_stop_thresh)) {
+ smp_mb();
+ if (likely(!efx->loopback_selftest))
+ netif_tx_start_queue(txq1->core_txq);
+ }
+}
+
/*
* Add a socket buffer to a TX queue
*
@@ -151,7 +193,7 @@
* This function is split out from efx_hard_start_xmit to allow the
* loopback test to direct packets via specific TX queues.
*
- * Returns NETDEV_TX_OK or NETDEV_TX_BUSY
+ * Returns NETDEV_TX_OK.
* You must hold netif_tx_lock() to call this function.
*/
netdev_tx_t efx_enqueue_skb(struct efx_tx_queue *tx_queue, struct sk_buff *skb)
@@ -160,12 +202,11 @@
struct device *dma_dev = &efx->pci_dev->dev;
struct efx_tx_buffer *buffer;
skb_frag_t *fragment;
- unsigned int len, unmap_len = 0, fill_level, insert_ptr;
+ unsigned int len, unmap_len = 0, insert_ptr;
dma_addr_t dma_addr, unmap_addr = 0;
unsigned int dma_len;
unsigned short dma_flags;
- int q_space, i = 0;
- netdev_tx_t rc = NETDEV_TX_OK;
+ int i = 0;
EFX_BUG_ON_PARANOID(tx_queue->write_count != tx_queue->insert_count);
@@ -183,9 +224,6 @@
return NETDEV_TX_OK;
}
- fill_level = tx_queue->insert_count - tx_queue->old_read_count;
- q_space = efx->txq_entries - 1 - fill_level;
-
/* Map for DMA. Use dma_map_single rather than dma_map_page
* since this is more efficient on machines with sparse
* memory.
@@ -205,32 +243,6 @@
/* Add to TX queue, splitting across DMA boundaries */
do {
- if (unlikely(q_space-- <= 0)) {
- /* It might be that completions have
- * happened since the xmit path last
- * checked. Update the xmit path's
- * copy of read_count.
- */
- netif_tx_stop_queue(tx_queue->core_txq);
- /* This memory barrier protects the
- * change of queue state from the access
- * of read_count. */
- smp_mb();
- tx_queue->old_read_count =
- ACCESS_ONCE(tx_queue->read_count);
- fill_level = (tx_queue->insert_count
- - tx_queue->old_read_count);
- q_space = efx->txq_entries - 1 - fill_level;
- if (unlikely(q_space-- <= 0)) {
- rc = NETDEV_TX_BUSY;
- goto unwind;
- }
- smp_mb();
- if (likely(!efx->loopback_selftest))
- netif_tx_start_queue(
- tx_queue->core_txq);
- }
-
insert_ptr = tx_queue->insert_count & tx_queue->ptr_mask;
buffer = &tx_queue->buffer[insert_ptr];
efx_tsoh_free(tx_queue, buffer);
@@ -277,6 +289,8 @@
/* Pass off to hardware */
efx_nic_push_buffers(tx_queue);
+ efx_tx_maybe_stop_queue(tx_queue);
+
return NETDEV_TX_OK;
dma_err:
@@ -288,7 +302,6 @@
/* Mark the packet as transmitted, and free the SKB ourselves */
dev_kfree_skb_any(skb);
- unwind:
/* Work backwards until we hit the original insert pointer value */
while (tx_queue->insert_count != tx_queue->write_count) {
unsigned int pkts_compl = 0, bytes_compl = 0;
@@ -309,7 +322,7 @@
DMA_TO_DEVICE);
}
- return rc;
+ return NETDEV_TX_OK;
}
/* Remove packets from the TX queue
@@ -448,6 +461,7 @@
{
unsigned fill_level;
struct efx_nic *efx = tx_queue->efx;
+ struct efx_tx_queue *txq2;
unsigned int pkts_compl = 0, bytes_compl = 0;
EFX_BUG_ON_PARANOID(index > tx_queue->ptr_mask);
@@ -455,15 +469,18 @@
efx_dequeue_buffers(tx_queue, index, &pkts_compl, &bytes_compl);
netdev_tx_completed_queue(tx_queue->core_txq, pkts_compl, bytes_compl);
- /* See if we need to restart the netif queue. This barrier
- * separates the update of read_count from the test of the
- * queue state. */
+ /* See if we need to restart the netif queue. This memory
+ * barrier ensures that we write read_count (inside
+ * efx_dequeue_buffers()) before reading the queue status.
+ */
smp_mb();
if (unlikely(netif_tx_queue_stopped(tx_queue->core_txq)) &&
likely(efx->port_enabled) &&
likely(netif_device_present(efx->net_dev))) {
- fill_level = tx_queue->insert_count - tx_queue->read_count;
- if (fill_level < EFX_TXQ_THRESHOLD(efx))
+ txq2 = efx_tx_queue_partner(tx_queue);
+ fill_level = max(tx_queue->insert_count - tx_queue->read_count,
+ txq2->insert_count - txq2->read_count);
+ if (fill_level <= efx->txq_wake_thresh)
netif_tx_wake_queue(tx_queue->core_txq);
}
@@ -776,47 +793,19 @@
* @len: Length of fragment
* @final_buffer: The final buffer inserted into the queue
*
- * Push descriptors onto the TX queue. Return 0 on success or 1 if
- * @tx_queue full.
+ * Push descriptors onto the TX queue.
*/
-static int efx_tx_queue_insert(struct efx_tx_queue *tx_queue,
- dma_addr_t dma_addr, unsigned len,
- struct efx_tx_buffer **final_buffer)
+static void efx_tx_queue_insert(struct efx_tx_queue *tx_queue,
+ dma_addr_t dma_addr, unsigned len,
+ struct efx_tx_buffer **final_buffer)
{
struct efx_tx_buffer *buffer;
struct efx_nic *efx = tx_queue->efx;
- unsigned dma_len, fill_level, insert_ptr;
- int q_space;
+ unsigned dma_len, insert_ptr;
EFX_BUG_ON_PARANOID(len <= 0);
- fill_level = tx_queue->insert_count - tx_queue->old_read_count;
- /* -1 as there is no way to represent all descriptors used */
- q_space = efx->txq_entries - 1 - fill_level;
-
while (1) {
- if (unlikely(q_space-- <= 0)) {
- /* It might be that completions have happened
- * since the xmit path last checked. Update
- * the xmit path's copy of read_count.
- */
- netif_tx_stop_queue(tx_queue->core_txq);
- /* This memory barrier protects the change of
- * queue state from the access of read_count. */
- smp_mb();
- tx_queue->old_read_count =
- ACCESS_ONCE(tx_queue->read_count);
- fill_level = (tx_queue->insert_count
- - tx_queue->old_read_count);
- q_space = efx->txq_entries - 1 - fill_level;
- if (unlikely(q_space-- <= 0)) {
- *final_buffer = NULL;
- return 1;
- }
- smp_mb();
- netif_tx_start_queue(tx_queue->core_txq);
- }
-
insert_ptr = tx_queue->insert_count & tx_queue->ptr_mask;
buffer = &tx_queue->buffer[insert_ptr];
++tx_queue->insert_count;
@@ -847,7 +836,6 @@
EFX_BUG_ON_PARANOID(!len);
buffer->len = len;
*final_buffer = buffer;
- return 0;
}
@@ -975,20 +963,19 @@
* @st: TSO state
*
* Form descriptors for the current fragment, until we reach the end
- * of fragment or end-of-packet. Return 0 on success, 1 if not enough
- * space in @tx_queue.
+ * of fragment or end-of-packet.
*/
-static int tso_fill_packet_with_fragment(struct efx_tx_queue *tx_queue,
- const struct sk_buff *skb,
- struct tso_state *st)
+static void tso_fill_packet_with_fragment(struct efx_tx_queue *tx_queue,
+ const struct sk_buff *skb,
+ struct tso_state *st)
{
struct efx_tx_buffer *buffer;
- int n, rc;
+ int n;
if (st->in_len == 0)
- return 0;
+ return;
if (st->packet_space == 0)
- return 0;
+ return;
EFX_BUG_ON_PARANOID(st->in_len <= 0);
EFX_BUG_ON_PARANOID(st->packet_space <= 0);
@@ -999,26 +986,24 @@
st->out_len -= n;
st->in_len -= n;
- rc = efx_tx_queue_insert(tx_queue, st->dma_addr, n, &buffer);
- if (likely(rc == 0)) {
- if (st->out_len == 0) {
- /* Transfer ownership of the skb */
- buffer->skb = skb;
- buffer->flags = EFX_TX_BUF_SKB;
- } else if (st->packet_space != 0) {
- buffer->flags = EFX_TX_BUF_CONT;
- }
+ efx_tx_queue_insert(tx_queue, st->dma_addr, n, &buffer);
- if (st->in_len == 0) {
- /* Transfer ownership of the DMA mapping */
- buffer->unmap_len = st->unmap_len;
- buffer->flags |= st->dma_flags;
- st->unmap_len = 0;
- }
+ if (st->out_len == 0) {
+ /* Transfer ownership of the skb */
+ buffer->skb = skb;
+ buffer->flags = EFX_TX_BUF_SKB;
+ } else if (st->packet_space != 0) {
+ buffer->flags = EFX_TX_BUF_CONT;
+ }
+
+ if (st->in_len == 0) {
+ /* Transfer ownership of the DMA mapping */
+ buffer->unmap_len = st->unmap_len;
+ buffer->flags |= st->dma_flags;
+ st->unmap_len = 0;
}
st->dma_addr += n;
- return rc;
}
@@ -1112,13 +1097,13 @@
*
* Add socket buffer @skb to @tx_queue, doing TSO or return != 0 if
* @skb was not enqueued. In all cases @skb is consumed. Return
- * %NETDEV_TX_OK or %NETDEV_TX_BUSY.
+ * %NETDEV_TX_OK.
*/
static int efx_enqueue_skb_tso(struct efx_tx_queue *tx_queue,
struct sk_buff *skb)
{
struct efx_nic *efx = tx_queue->efx;
- int frag_i, rc, rc2 = NETDEV_TX_OK;
+ int frag_i, rc;
struct tso_state state;
/* Find the packet protocol and sanity-check it */
@@ -1150,11 +1135,7 @@
goto mem_err;
while (1) {
- rc = tso_fill_packet_with_fragment(tx_queue, skb, &state);
- if (unlikely(rc)) {
- rc2 = NETDEV_TX_BUSY;
- goto unwind;
- }
+ tso_fill_packet_with_fragment(tx_queue, skb, &state);
/* Move onto the next fragment? */
if (state.in_len == 0) {
@@ -1178,6 +1159,8 @@
/* Pass off to hardware */
efx_nic_push_buffers(tx_queue);
+ efx_tx_maybe_stop_queue(tx_queue);
+
tx_queue->tso_bursts++;
return NETDEV_TX_OK;
@@ -1186,7 +1169,6 @@
"Out of memory for TSO headers, or DMA mapping error\n");
dev_kfree_skb_any(skb);
- unwind:
/* Free the DMA mapping we were in the process of writing out */
if (state.unmap_len) {
if (state.dma_flags & EFX_TX_BUF_MAP_SINGLE)
@@ -1198,7 +1180,7 @@
}
efx_enqueue_unwind(tx_queue);
- return rc2;
+ return NETDEV_TX_OK;
}