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Date: Mon, 31 Oct 2016 15:29:48 -0700
From: Jeff Kirsher <jeffrey.t.kirsher@...el.com>
To: davem@...emloft.net
Cc: Alexander Duyck <alexander.h.duyck@...el.com>,
netdev@...r.kernel.org, nhorman@...hat.com, sassmann@...hat.com,
jogreene@...hat.com, guru.anbalagane@...cle.com,
Jeff Kirsher <jeffrey.t.kirsher@...el.com>
Subject: [net-next 18/22] i40e: Reorder logic for coalescing RS bits
From: Alexander Duyck <alexander.h.duyck@...el.com>
This patch reorders the logic at the end of i40e_tx_map to address the
fact that the logic was rather convoluted and much larger than it needed
to be.
In order to try and coalesce the code paths I have updated some of the
comments and repurposed some of the variables in order to reduce
unnecessary overhead.
This patch does the following:
1. Quit tracking skb->xmit_more with a flag, just max out packet_stride
2. Drop tail_bump and do_rs and instead just use desc_count and td_cmd
3. Pull comments from ixgbe that make need for wmb() more explicit.
Change-ID: Ic7da85ec75043c634e87fef958109789bcc6317c
Signed-off-by: Alexander Duyck <alexander.h.duyck@...el.com>
Tested-by: Andrew Bowers <andrewx.bowers@...el.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@...el.com>
---
drivers/net/ethernet/intel/i40e/i40e_txrx.c | 105 +++++++++++++-------------
drivers/net/ethernet/intel/i40e/i40e_txrx.h | 1 -
drivers/net/ethernet/intel/i40evf/i40e_txrx.c | 105 +++++++++++++-------------
drivers/net/ethernet/intel/i40evf/i40e_txrx.h | 1 -
4 files changed, 108 insertions(+), 104 deletions(-)
diff --git a/drivers/net/ethernet/intel/i40e/i40e_txrx.c b/drivers/net/ethernet/intel/i40e/i40e_txrx.c
index 75b8f5b..5544b50 100644
--- a/drivers/net/ethernet/intel/i40e/i40e_txrx.c
+++ b/drivers/net/ethernet/intel/i40e/i40e_txrx.c
@@ -616,7 +616,7 @@ u32 i40e_get_tx_pending(struct i40e_ring *ring, bool in_sw)
return 0;
}
-#define WB_STRIDE 0x3
+#define WB_STRIDE 4
/**
* i40e_clean_tx_irq - Reclaim resources after transmit completes
@@ -732,7 +732,7 @@ static bool i40e_clean_tx_irq(struct i40e_vsi *vsi,
unsigned int j = i40e_get_tx_pending(tx_ring, false);
if (budget &&
- ((j / (WB_STRIDE + 1)) == 0) && (j != 0) &&
+ ((j / WB_STRIDE) == 0) && (j > 0) &&
!test_bit(__I40E_DOWN, &vsi->state) &&
(I40E_DESC_UNUSED(tx_ring) != tx_ring->count))
tx_ring->arm_wb = true;
@@ -2700,9 +2700,7 @@ static inline void i40e_tx_map(struct i40e_ring *tx_ring, struct sk_buff *skb,
u32 td_tag = 0;
dma_addr_t dma;
u16 gso_segs;
- u16 desc_count = 0;
- bool tail_bump = true;
- bool do_rs = false;
+ u16 desc_count = 1;
if (tx_flags & I40E_TX_FLAGS_HW_VLAN) {
td_cmd |= I40E_TX_DESC_CMD_IL2TAG1;
@@ -2785,8 +2783,7 @@ static inline void i40e_tx_map(struct i40e_ring *tx_ring, struct sk_buff *skb,
tx_bi = &tx_ring->tx_bi[i];
}
- /* set next_to_watch value indicating a packet is present */
- first->next_to_watch = tx_desc;
+ netdev_tx_sent_queue(txring_txq(tx_ring), first->bytecount);
i++;
if (i == tx_ring->count)
@@ -2794,66 +2791,72 @@ static inline void i40e_tx_map(struct i40e_ring *tx_ring, struct sk_buff *skb,
tx_ring->next_to_use = i;
- netdev_tx_sent_queue(txring_txq(tx_ring), first->bytecount);
i40e_maybe_stop_tx(tx_ring, DESC_NEEDED);
+ /* write last descriptor with EOP bit */
+ td_cmd |= I40E_TX_DESC_CMD_EOP;
+
+ /* We can OR these values together as they both are checked against
+ * 4 below and at this point desc_count will be used as a boolean value
+ * after this if/else block.
+ */
+ desc_count |= ++tx_ring->packet_stride;
+
/* Algorithm to optimize tail and RS bit setting:
- * if xmit_more is supported
- * if xmit_more is true
- * do not update tail and do not mark RS bit.
- * if xmit_more is false and last xmit_more was false
- * if every packet spanned less than 4 desc
- * then set RS bit on 4th packet and update tail
- * on every packet
- * else
- * update tail and set RS bit on every packet.
- * if xmit_more is false and last_xmit_more was true
- * update tail and set RS bit.
+ * if queue is stopped
+ * mark RS bit
+ * reset packet counter
+ * else if xmit_more is supported and is true
+ * advance packet counter to 4
+ * reset desc_count to 0
*
- * Optimization: wmb to be issued only in case of tail update.
- * Also optimize the Descriptor WB path for RS bit with the same
- * algorithm.
+ * if desc_count >= 4
+ * mark RS bit
+ * reset packet counter
+ * if desc_count > 0
+ * update tail
*
- * Note: If there are less than 4 packets
+ * Note: If there are less than 4 descriptors
* pending and interrupts were disabled the service task will
* trigger a force WB.
*/
- if (skb->xmit_more &&
- !netif_xmit_stopped(txring_txq(tx_ring))) {
- tx_ring->flags |= I40E_TXR_FLAGS_LAST_XMIT_MORE_SET;
- tail_bump = false;
- } else if (!skb->xmit_more &&
- !netif_xmit_stopped(txring_txq(tx_ring)) &&
- (!(tx_ring->flags & I40E_TXR_FLAGS_LAST_XMIT_MORE_SET)) &&
- (tx_ring->packet_stride < WB_STRIDE) &&
- (desc_count < WB_STRIDE)) {
- tx_ring->packet_stride++;
- } else {
+ if (netif_xmit_stopped(txring_txq(tx_ring))) {
+ goto do_rs;
+ } else if (skb->xmit_more) {
+ /* set stride to arm on next packet and reset desc_count */
+ tx_ring->packet_stride = WB_STRIDE;
+ desc_count = 0;
+ } else if (desc_count >= WB_STRIDE) {
+do_rs:
+ /* write last descriptor with RS bit set */
+ td_cmd |= I40E_TX_DESC_CMD_RS;
tx_ring->packet_stride = 0;
- tx_ring->flags &= ~I40E_TXR_FLAGS_LAST_XMIT_MORE_SET;
- do_rs = true;
}
- if (do_rs)
- tx_ring->packet_stride = 0;
tx_desc->cmd_type_offset_bsz =
- build_ctob(td_cmd, td_offset, size, td_tag) |
- cpu_to_le64((u64)(do_rs ? I40E_TXD_CMD :
- I40E_TX_DESC_CMD_EOP) <<
- I40E_TXD_QW1_CMD_SHIFT);
+ build_ctob(td_cmd, td_offset, size, td_tag);
+
+ /* Force memory writes to complete before letting h/w know there
+ * are new descriptors to fetch.
+ *
+ * We also use this memory barrier to make certain all of the
+ * status bits have been updated before next_to_watch is written.
+ */
+ wmb();
+
+ /* set next_to_watch value indicating a packet is present */
+ first->next_to_watch = tx_desc;
/* notify HW of packet */
- if (!tail_bump) {
- prefetchw(tx_desc + 1);
- } else {
- /* Force memory writes to complete before letting h/w
- * know there are new descriptors to fetch. (Only
- * applicable for weak-ordered memory model archs,
- * such as IA-64).
- */
- wmb();
+ if (desc_count) {
writel(i, tx_ring->tail);
+
+ /* we need this if more than one processor can write to our tail
+ * at a time, it synchronizes IO on IA64/Altix systems
+ */
+ mmiowb();
}
+
return;
dma_error:
diff --git a/drivers/net/ethernet/intel/i40e/i40e_txrx.h b/drivers/net/ethernet/intel/i40e/i40e_txrx.h
index 42f04d6..de8550f 100644
--- a/drivers/net/ethernet/intel/i40e/i40e_txrx.h
+++ b/drivers/net/ethernet/intel/i40e/i40e_txrx.h
@@ -313,7 +313,6 @@ struct i40e_ring {
u16 flags;
#define I40E_TXR_FLAGS_WB_ON_ITR BIT(0)
-#define I40E_TXR_FLAGS_LAST_XMIT_MORE_SET BIT(2)
/* stats structs */
struct i40e_queue_stats stats;
diff --git a/drivers/net/ethernet/intel/i40evf/i40e_txrx.c b/drivers/net/ethernet/intel/i40evf/i40e_txrx.c
index e2d3622..c4b174a 100644
--- a/drivers/net/ethernet/intel/i40evf/i40e_txrx.c
+++ b/drivers/net/ethernet/intel/i40evf/i40e_txrx.c
@@ -150,7 +150,7 @@ u32 i40evf_get_tx_pending(struct i40e_ring *ring, bool in_sw)
return 0;
}
-#define WB_STRIDE 0x3
+#define WB_STRIDE 4
/**
* i40e_clean_tx_irq - Reclaim resources after transmit completes
@@ -266,7 +266,7 @@ static bool i40e_clean_tx_irq(struct i40e_vsi *vsi,
unsigned int j = i40evf_get_tx_pending(tx_ring, false);
if (budget &&
- ((j / (WB_STRIDE + 1)) == 0) && (j > 0) &&
+ ((j / WB_STRIDE) == 0) && (j > 0) &&
!test_bit(__I40E_DOWN, &vsi->state) &&
(I40E_DESC_UNUSED(tx_ring) != tx_ring->count))
tx_ring->arm_wb = true;
@@ -1950,9 +1950,7 @@ static inline void i40evf_tx_map(struct i40e_ring *tx_ring, struct sk_buff *skb,
u32 td_tag = 0;
dma_addr_t dma;
u16 gso_segs;
- u16 desc_count = 0;
- bool tail_bump = true;
- bool do_rs = false;
+ u16 desc_count = 1;
if (tx_flags & I40E_TX_FLAGS_HW_VLAN) {
td_cmd |= I40E_TX_DESC_CMD_IL2TAG1;
@@ -2035,8 +2033,7 @@ static inline void i40evf_tx_map(struct i40e_ring *tx_ring, struct sk_buff *skb,
tx_bi = &tx_ring->tx_bi[i];
}
- /* set next_to_watch value indicating a packet is present */
- first->next_to_watch = tx_desc;
+ netdev_tx_sent_queue(txring_txq(tx_ring), first->bytecount);
i++;
if (i == tx_ring->count)
@@ -2044,66 +2041,72 @@ static inline void i40evf_tx_map(struct i40e_ring *tx_ring, struct sk_buff *skb,
tx_ring->next_to_use = i;
- netdev_tx_sent_queue(txring_txq(tx_ring), first->bytecount);
i40e_maybe_stop_tx(tx_ring, DESC_NEEDED);
+ /* write last descriptor with EOP bit */
+ td_cmd |= I40E_TX_DESC_CMD_EOP;
+
+ /* We can OR these values together as they both are checked against
+ * 4 below and at this point desc_count will be used as a boolean value
+ * after this if/else block.
+ */
+ desc_count |= ++tx_ring->packet_stride;
+
/* Algorithm to optimize tail and RS bit setting:
- * if xmit_more is supported
- * if xmit_more is true
- * do not update tail and do not mark RS bit.
- * if xmit_more is false and last xmit_more was false
- * if every packet spanned less than 4 desc
- * then set RS bit on 4th packet and update tail
- * on every packet
- * else
- * update tail and set RS bit on every packet.
- * if xmit_more is false and last_xmit_more was true
- * update tail and set RS bit.
+ * if queue is stopped
+ * mark RS bit
+ * reset packet counter
+ * else if xmit_more is supported and is true
+ * advance packet counter to 4
+ * reset desc_count to 0
*
- * Optimization: wmb to be issued only in case of tail update.
- * Also optimize the Descriptor WB path for RS bit with the same
- * algorithm.
+ * if desc_count >= 4
+ * mark RS bit
+ * reset packet counter
+ * if desc_count > 0
+ * update tail
*
- * Note: If there are less than 4 packets
+ * Note: If there are less than 4 descriptors
* pending and interrupts were disabled the service task will
* trigger a force WB.
*/
- if (skb->xmit_more &&
- !netif_xmit_stopped(txring_txq(tx_ring))) {
- tx_ring->flags |= I40E_TXR_FLAGS_LAST_XMIT_MORE_SET;
- tail_bump = false;
- } else if (!skb->xmit_more &&
- !netif_xmit_stopped(txring_txq(tx_ring)) &&
- (!(tx_ring->flags & I40E_TXR_FLAGS_LAST_XMIT_MORE_SET)) &&
- (tx_ring->packet_stride < WB_STRIDE) &&
- (desc_count < WB_STRIDE)) {
- tx_ring->packet_stride++;
- } else {
+ if (netif_xmit_stopped(txring_txq(tx_ring))) {
+ goto do_rs;
+ } else if (skb->xmit_more) {
+ /* set stride to arm on next packet and reset desc_count */
+ tx_ring->packet_stride = WB_STRIDE;
+ desc_count = 0;
+ } else if (desc_count >= WB_STRIDE) {
+do_rs:
+ /* write last descriptor with RS bit set */
+ td_cmd |= I40E_TX_DESC_CMD_RS;
tx_ring->packet_stride = 0;
- tx_ring->flags &= ~I40E_TXR_FLAGS_LAST_XMIT_MORE_SET;
- do_rs = true;
}
- if (do_rs)
- tx_ring->packet_stride = 0;
tx_desc->cmd_type_offset_bsz =
- build_ctob(td_cmd, td_offset, size, td_tag) |
- cpu_to_le64((u64)(do_rs ? I40E_TXD_CMD :
- I40E_TX_DESC_CMD_EOP) <<
- I40E_TXD_QW1_CMD_SHIFT);
+ build_ctob(td_cmd, td_offset, size, td_tag);
+
+ /* Force memory writes to complete before letting h/w know there
+ * are new descriptors to fetch.
+ *
+ * We also use this memory barrier to make certain all of the
+ * status bits have been updated before next_to_watch is written.
+ */
+ wmb();
+
+ /* set next_to_watch value indicating a packet is present */
+ first->next_to_watch = tx_desc;
/* notify HW of packet */
- if (!tail_bump) {
- prefetchw(tx_desc + 1);
- } else {
- /* Force memory writes to complete before letting h/w
- * know there are new descriptors to fetch. (Only
- * applicable for weak-ordered memory model archs,
- * such as IA-64).
- */
- wmb();
+ if (desc_count) {
writel(i, tx_ring->tail);
+
+ /* we need this if more than one processor can write to our tail
+ * at a time, it synchronizes IO on IA64/Altix systems
+ */
+ mmiowb();
}
+
return;
dma_error:
diff --git a/drivers/net/ethernet/intel/i40evf/i40e_txrx.h b/drivers/net/ethernet/intel/i40evf/i40e_txrx.h
index abcdeca..a586e19 100644
--- a/drivers/net/ethernet/intel/i40evf/i40e_txrx.h
+++ b/drivers/net/ethernet/intel/i40evf/i40e_txrx.h
@@ -309,7 +309,6 @@ struct i40e_ring {
bool ring_active; /* is ring online or not */
bool arm_wb; /* do something to arm write back */
u8 packet_stride;
-#define I40E_TXR_FLAGS_LAST_XMIT_MORE_SET BIT(2)
u16 flags;
#define I40E_TXR_FLAGS_WB_ON_ITR BIT(0)
--
2.7.4
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