Commit 14bf718f authored by Ben Hutchings's avatar Ben Hutchings
Browse files

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: default avatarBen Hutchings <bhutchings@solarflare.com>
parent 7668ff9c

drivers/net/ethernet/sfc/efx.c

+10 −0
Original line number Diff line number Diff line
@@ -630,6 +630,16 @@ static void efx_start_datapath(struct efx_nic *efx) 
	efx->rx_buffer_order = get_order(efx->rx_buffer_len +

					 sizeof(struct efx_rx_page_state));



	/* We must keep at least one descriptor in a TX ring empty.

	 * We could avoid this when the queue size does not exactly

	 * match the hardware ring size, but it's not that important.

	 * Therefore we stop the queue when one more skb might fill

	 * the ring completely.  We wake it when half way back to

	 * empty.

	 */

	efx->txq_stop_thresh = efx->txq_entries - efx_tx_max_skb_descs(efx);

	efx->txq_wake_thresh = efx->txq_stop_thresh / 2;



	/* Initialise the channels */

	efx_for_each_channel(channel, efx) {

		efx_for_each_channel_tx_queue(tx_queue, channel)

drivers/net/ethernet/sfc/net_driver.h

+5 −0
Original line number Diff line number Diff line
@@ -665,6 +665,8 @@ struct vfdi_status; 
 *	should be allocated for this NIC

 * @rxq_entries: Size of receive queues requested by user.

 * @txq_entries: Size of transmit queues requested by user.

 * @txq_stop_thresh: TX queue fill level at or above which we stop it.

 * @txq_wake_thresh: TX queue fill level at or below which we wake it.

 * @tx_dc_base: Base qword address in SRAM of TX queue descriptor caches

 * @rx_dc_base: Base qword address in SRAM of RX queue descriptor caches

 * @sram_lim_qw: Qword address limit of SRAM
@@ -775,6 +777,9 @@ struct efx_nic { 


	unsigned rxq_entries;

	unsigned txq_entries;

	unsigned int txq_stop_thresh;

	unsigned int txq_wake_thresh;



	unsigned tx_dc_base;

	unsigned rx_dc_base;

	unsigned sram_lim_qw;

drivers/net/ethernet/sfc/tx.c

+97 −115
Original line number Diff line number Diff line
@@ -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 @@ unsigned int efx_tx_max_skb_descs(struct efx_nic *efx) 
	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 @@ unsigned int efx_tx_max_skb_descs(struct efx_nic *efx) 
 * 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 @@ netdev_tx_t efx_enqueue_skb(struct efx_tx_queue *tx_queue, struct sk_buff *skb) 
	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 @@ netdev_tx_t efx_enqueue_skb(struct efx_tx_queue *tx_queue, struct sk_buff *skb) 
			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 @@ netdev_tx_t efx_enqueue_skb(struct efx_tx_queue *tx_queue, struct sk_buff *skb) 


		/* 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 @@ netdev_tx_t efx_enqueue_skb(struct efx_tx_queue *tx_queue, struct sk_buff *skb) 
	/* 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 @@ netdev_tx_t efx_enqueue_skb(struct efx_tx_queue *tx_queue, struct sk_buff *skb) 
	/* 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 @@ netdev_tx_t efx_enqueue_skb(struct efx_tx_queue *tx_queue, struct sk_buff *skb) 
				       DMA_TO_DEVICE);

	}



	return rc;

	return NETDEV_TX_OK;

}



/* Remove packets from the TX queue
@@ -448,6 +461,7 @@ void efx_xmit_done(struct efx_tx_queue *tx_queue, unsigned int index) 
{

	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 @@ void efx_xmit_done(struct efx_tx_queue *tx_queue, unsigned int index) 
	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 @@ efx_tsoh_heap_free(struct efx_tx_queue *tx_queue, struct efx_tso_header *tsoh) 
 * @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,

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 @@ static int efx_tx_queue_insert(struct efx_tx_queue *tx_queue, 
	EFX_BUG_ON_PARANOID(!len);

	buffer->len = len;

	*final_buffer = buffer;

	return 0;

}
@@ -975,20 +963,19 @@ static int tso_get_head_fragment(struct tso_state *st, struct efx_nic *efx, 
 * @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,

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);
@@ -999,8 +986,8 @@ static int tso_fill_packet_with_fragment(struct efx_tx_queue *tx_queue, 
	st->out_len -= n;

	st->in_len -= n;



	rc = efx_tx_queue_insert(tx_queue, st->dma_addr, n, &buffer);

	if (likely(rc == 0)) {

	efx_tx_queue_insert(tx_queue, st->dma_addr, n, &buffer);



	if (st->out_len == 0) {

		/* Transfer ownership of the skb */

		buffer->skb = skb;
@@ -1015,10 +1002,8 @@ static int tso_fill_packet_with_fragment(struct efx_tx_queue *tx_queue, 
		buffer->flags |= st->dma_flags;

		st->unmap_len = 0;

	}

	}



	st->dma_addr += n;

	return rc;

}
@@ -1112,13 +1097,13 @@ static int tso_start_new_packet(struct efx_tx_queue *tx_queue, 
 *

 * 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 @@ static int efx_enqueue_skb_tso(struct efx_tx_queue *tx_queue, 
		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 @@ static int efx_enqueue_skb_tso(struct efx_tx_queue *tx_queue, 
	/* 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 @@ static int efx_enqueue_skb_tso(struct efx_tx_queue *tx_queue, 
		  "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 @@ static int efx_enqueue_skb_tso(struct efx_tx_queue *tx_queue, 
	}



	efx_enqueue_unwind(tx_queue);

	return rc2;

	return NETDEV_TX_OK;

}