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Message-ID: <alpine.LFD.2.03.1410141933500.26972@solarflare.com>
Date: Tue, 14 Oct 2014 19:41:37 +0100
From: Edward Cree <ecree@...arflare.com>
To: Daniel Borkmann <dborkman@...hat.com>
CC: Edward Cree <ecree@...arflare.com>, <davem@...emloft.net>,
<nikolay@...hat.com>, <netdev@...r.kernel.org>,
Shradha Shah <sshah@...arflare.com>,
Jon Cooper <jcooper@...arflare.com>,
linux-net-drivers <linux-net-drivers@...arflare.com>
Subject: [PATCH RFC net-next] sfc: add support for skb->xmit_more
Don't ring the doorbell, and don't do PIO. This will also prevent
TX Push, because there will be more than one buffer waiting when
the doorbell is rung.
Signed-off-by: Edward Cree <ecree@...arflare.com>
---
drivers/net/ethernet/sfc/nic.h | 29 +++++++++++++++++++++++-----
drivers/net/ethernet/sfc/tx.c | 43 +++++++++++++++++-------------------------
2 files changed, 41 insertions(+), 31 deletions(-)
diff --git a/drivers/net/ethernet/sfc/nic.h b/drivers/net/ethernet/sfc/nic.h
index 60f8514..f77cce0 100644
--- a/drivers/net/ethernet/sfc/nic.h
+++ b/drivers/net/ethernet/sfc/nic.h
@@ -71,9 +71,17 @@ efx_tx_desc(struct efx_tx_queue *tx_queue, unsigned int index)
return ((efx_qword_t *) (tx_queue->txd.buf.addr)) + index;
}
-/* Report whether the NIC considers this TX queue empty, given the
- * write_count used for the last doorbell push. May return false
- * negative.
+/* 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;
+}
+
+/* Report whether this TX queue would be empty for the given write_count.
+ * May return false negative.
*/
static inline bool __efx_nic_tx_is_empty(struct efx_tx_queue *tx_queue,
unsigned int write_count)
@@ -86,9 +94,18 @@ static inline bool __efx_nic_tx_is_empty(struct efx_tx_queue *tx_queue,
return ((empty_read_count ^ write_count) & ~EFX_EMPTY_COUNT_VALID) == 0;
}
-static inline bool efx_nic_tx_is_empty(struct efx_tx_queue *tx_queue)
+/* Decide whether we can use TX PIO, ie. write packet data directly into
+ * a buffer on the device. This can reduce latency at the expense of
+ * throughput, so we only do this if both hardware and software TX rings
+ * are empty. This also ensures that only one packet at a time can be
+ * using the PIO buffer.
+ */
+static inline bool efx_nic_may_tx_pio(struct efx_tx_queue *tx_queue)
{
- return __efx_nic_tx_is_empty(tx_queue, tx_queue->write_count);
+ struct efx_tx_queue *partner = efx_tx_queue_partner(tx_queue);
+ return tx_queue->piobuf &&
+ __efx_nic_tx_is_empty(tx_queue, tx_queue->insert_count) &&
+ __efx_nic_tx_is_empty(partner, partner->insert_count);
}
/* Decide whether to push a TX descriptor to the NIC vs merely writing
@@ -96,6 +113,8 @@ static inline bool efx_nic_tx_is_empty(struct efx_tx_queue *tx_queue)
* descriptor to an empty queue, but is otherwise pointless. Further,
* Falcon and Siena have hardware bugs (SF bug 33851) that may be
* triggered if we don't check this.
+ * We use the write_count used for the last doorbell push, to get the
+ * NIC's view of the tx queue.
*/
static inline bool efx_nic_may_push_tx_desc(struct efx_tx_queue *tx_queue,
unsigned int write_count)
diff --git a/drivers/net/ethernet/sfc/tx.c b/drivers/net/ethernet/sfc/tx.c
index 3206098..aaf2987 100644
--- a/drivers/net/ethernet/sfc/tx.c
+++ b/drivers/net/ethernet/sfc/tx.c
@@ -132,15 +132,6 @@ 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 */
@@ -344,6 +335,7 @@ netdev_tx_t efx_enqueue_skb(struct efx_tx_queue *tx_queue, struct sk_buff *skb)
struct efx_nic *efx = tx_queue->efx;
struct device *dma_dev = &efx->pci_dev->dev;
struct efx_tx_buffer *buffer;
+ unsigned int old_insert_count = tx_queue->insert_count;
skb_frag_t *fragment;
unsigned int len, unmap_len = 0;
dma_addr_t dma_addr, unmap_addr = 0;
@@ -351,8 +343,6 @@ netdev_tx_t efx_enqueue_skb(struct efx_tx_queue *tx_queue, struct sk_buff *skb)
unsigned short dma_flags;
int i = 0;
- EFX_BUG_ON_PARANOID(tx_queue->write_count != tx_queue->insert_count);
-
if (skb_shinfo(skb)->gso_size)
return efx_enqueue_skb_tso(tx_queue, skb);
@@ -369,9 +359,8 @@ netdev_tx_t efx_enqueue_skb(struct efx_tx_queue *tx_queue, struct sk_buff *skb)
/* Consider using PIO for short packets */
#ifdef EFX_USE_PIO
- if (skb->len <= efx_piobuf_size && tx_queue->piobuf &&
- efx_nic_tx_is_empty(tx_queue) &&
- efx_nic_tx_is_empty(efx_tx_queue_partner(tx_queue))) {
+ if (skb->len <= efx_piobuf_size && !skb->xmit_more &&
+ efx_nic_may_tx_pio(tx_queue)) {
buffer = efx_enqueue_skb_pio(tx_queue, skb);
dma_flags = EFX_TX_BUF_OPTION;
goto finish_packet;
@@ -439,13 +428,14 @@ finish_packet:
netdev_tx_sent_queue(tx_queue->core_txq, skb->len);
+ efx_tx_maybe_stop_queue(tx_queue);
+
/* Pass off to hardware */
- efx_nic_push_buffers(tx_queue);
+ if (!skb->xmit_more || netif_xmit_stopped(tx_queue->core_txq))
+ efx_nic_push_buffers(tx_queue);
tx_queue->tx_packets++;
- efx_tx_maybe_stop_queue(tx_queue);
-
return NETDEV_TX_OK;
dma_err:
@@ -458,7 +448,7 @@ finish_packet:
dev_kfree_skb_any(skb);
/* Work backwards until we hit the original insert pointer value */
- while (tx_queue->insert_count != tx_queue->write_count) {
+ while (tx_queue->insert_count != old_insert_count) {
unsigned int pkts_compl = 0, bytes_compl = 0;
--tx_queue->insert_count;
buffer = __efx_tx_queue_get_insert_buffer(tx_queue);
@@ -989,12 +979,13 @@ static int efx_tso_put_header(struct efx_tx_queue *tx_queue,
/* Remove buffers put into a tx_queue. None of the buffers must have
* an skb attached.
*/
-static void efx_enqueue_unwind(struct efx_tx_queue *tx_queue)
+static void efx_enqueue_unwind(struct efx_tx_queue *tx_queue,
+ unsigned int insert_count)
{
struct efx_tx_buffer *buffer;
/* Work backwards until we hit the original insert pointer value */
- while (tx_queue->insert_count != tx_queue->write_count) {
+ while (tx_queue->insert_count != insert_count) {
--tx_queue->insert_count;
buffer = __efx_tx_queue_get_insert_buffer(tx_queue);
efx_dequeue_buffer(tx_queue, buffer, NULL, NULL);
@@ -1258,14 +1249,13 @@ static int efx_enqueue_skb_tso(struct efx_tx_queue *tx_queue,
struct sk_buff *skb)
{
struct efx_nic *efx = tx_queue->efx;
+ unsigned int old_insert_count = tx_queue->insert_count;
int frag_i, rc;
struct tso_state state;
/* Find the packet protocol and sanity-check it */
state.protocol = efx_tso_check_protocol(skb);
- EFX_BUG_ON_PARANOID(tx_queue->write_count != tx_queue->insert_count);
-
rc = tso_start(&state, efx, skb);
if (rc)
goto mem_err;
@@ -1308,11 +1298,12 @@ static int efx_enqueue_skb_tso(struct efx_tx_queue *tx_queue,
netdev_tx_sent_queue(tx_queue->core_txq, skb->len);
- /* Pass off to hardware */
- efx_nic_push_buffers(tx_queue);
-
efx_tx_maybe_stop_queue(tx_queue);
+ /* Pass off to hardware */
+ if (!skb->xmit_more || netif_xmit_stopped(tx_queue->core_txq))
+ efx_nic_push_buffers(tx_queue);
+
tx_queue->tso_bursts++;
return NETDEV_TX_OK;
@@ -1336,6 +1327,6 @@ static int efx_enqueue_skb_tso(struct efx_tx_queue *tx_queue,
dma_unmap_single(&efx->pci_dev->dev, state.header_dma_addr,
state.header_unmap_len, DMA_TO_DEVICE);
- efx_enqueue_unwind(tx_queue);
+ efx_enqueue_unwind(tx_queue, old_insert_count);
return NETDEV_TX_OK;
}
--
1.7.11.7
--
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