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i40e: Reorder logic for coalescing RS bits 

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@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
This commit is contained in:
Alexander Duyck 2016-10-11 15:26:54 -07:00 committed by Jeff Kirsher
parent 4b8164467b
commit 1dc8b53879
4 changed files with 108 additions and 104 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

103
drivers/net/ethernet/intel/i40e/i40e_txrx.c
View File

@ -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);
/* 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).
/* 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 (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:

1
drivers/net/ethernet/intel/i40e/i40e_txrx.h
View File

@ -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;

103
drivers/net/ethernet/intel/i40evf/i40e_txrx.c
View File

@ -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);
/* 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).
/* 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 (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:

1
drivers/net/ethernet/intel/i40evf/i40e_txrx.h
View File

@ -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)