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i40e: Fix RS bit update in Tx path and disable force WB workaround

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This patch fixes the issue of forcing WB too often causing us to not
benefit from NAPI.

Without this patch we were forcing WB/arming interrupt too often taking
away the benefits of NAPI and causing a performance impact.

With this patch we disable force WB in the clean routine for X710
and XL710 adapters. X722 adapters do not enable interrupt to force
a WB and benefit from WB_ON_ITR and hence force WB is left enabled
for those adapters.
For XL710 and X710 adapters if we have less than 4 packets pending
a software Interrupt triggered from service task will force a WB.

This patch also changes the conditions for setting RS bit as described
in code comments. This optimizes when the HW does a tail bump and when
it does a WB. It also optimizes when we do a wmb.

Signed-off-by: Anjali Singhai Jain <anjali.singhai@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:
Anjali Singhai 2015-09-25 18:26:13 -07:00 committed by Jeff Kirsher
parent c1d1791dc8
commit 5804474311
2 changed files with 87 additions and 44 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

129
drivers/net/ethernet/intel/i40e/i40e_txrx.c
View File

@ -726,17 +726,22 @@ static bool i40e_clean_tx_irq(struct i40e_ring *tx_ring, int budget)
tx_ring->q_vector->tx.total_bytes += total_bytes;
tx_ring->q_vector->tx.total_packets += total_packets;
/* check to see if there are any non-cache aligned descriptors
* waiting to be written back, and kick the hardware to force
* them to be written back in case of napi polling
*/
if (budget &&
!((i & WB_STRIDE) == WB_STRIDE) &&
!test_bit(__I40E_DOWN, &tx_ring->vsi->state) &&
(I40E_DESC_UNUSED(tx_ring) != tx_ring->count))
tx_ring->arm_wb = true;
else
tx_ring->arm_wb = false;
if (tx_ring->flags & I40E_TXR_FLAGS_WB_ON_ITR) {
unsigned int j = 0;
/* check to see if there are < 4 descriptors
* waiting to be written back, then kick the hardware to force
* them to be written back in case we stay in NAPI.
* In this mode on X722 we do not enable Interrupt.
*/
j = i40e_get_tx_pending(tx_ring);
if (budget &&
((j / (WB_STRIDE + 1)) == 0) && (j != 0) &&
!test_bit(__I40E_DOWN, &tx_ring->vsi->state) &&
(I40E_DESC_UNUSED(tx_ring) != tx_ring->count))
tx_ring->arm_wb = true;
}
netdev_tx_completed_queue(netdev_get_tx_queue(tx_ring->netdev,
tx_ring->queue_index),
@ -2500,6 +2505,9 @@ 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;
if (tx_flags & I40E_TX_FLAGS_HW_VLAN) {
td_cmd |= I40E_TX_DESC_CMD_IL2TAG1;
@ -2540,6 +2548,8 @@ static inline void i40e_tx_map(struct i40e_ring *tx_ring, struct sk_buff *skb,
tx_desc++;
i++;
desc_count++;
if (i == tx_ring->count) {
tx_desc = I40E_TX_DESC(tx_ring, 0);
i = 0;
@ -2559,6 +2569,8 @@ static inline void i40e_tx_map(struct i40e_ring *tx_ring, struct sk_buff *skb,
tx_desc++;
i++;
desc_count++;
if (i == tx_ring->count) {
tx_desc = I40E_TX_DESC(tx_ring, 0);
i = 0;
@ -2573,34 +2585,6 @@ static inline void i40e_tx_map(struct i40e_ring *tx_ring, struct sk_buff *skb,
tx_bi = &tx_ring->tx_bi[i];
}
/* Place RS bit on last descriptor of any packet that spans across the
* 4th descriptor (WB_STRIDE aka 0x3) in a 64B cacheline.
*/
if (((i & WB_STRIDE) != WB_STRIDE) &&
(first <= &tx_ring->tx_bi[i]) &&
(first >= &tx_ring->tx_bi[i & ~WB_STRIDE])) {
tx_desc->cmd_type_offset_bsz =
build_ctob(td_cmd, td_offset, size, td_tag) |
cpu_to_le64((u64)I40E_TX_DESC_CMD_EOP <<
I40E_TXD_QW1_CMD_SHIFT);
} else {
tx_desc->cmd_type_offset_bsz =
build_ctob(td_cmd, td_offset, size, td_tag) |
cpu_to_le64((u64)I40E_TXD_CMD <<
I40E_TXD_QW1_CMD_SHIFT);
}
netdev_tx_sent_queue(netdev_get_tx_queue(tx_ring->netdev,
tx_ring->queue_index),
first->bytecount);
/* 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();
/* set next_to_watch value indicating a packet is present */
first->next_to_watch = tx_desc;
@ -2610,15 +2594,72 @@ 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(netdev_get_tx_queue(tx_ring->netdev,
tx_ring->queue_index),
first->bytecount);
i40e_maybe_stop_tx(tx_ring, DESC_NEEDED);
/* 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.
*
* Optimization: wmb to be issued only in case of tail update.
* Also optimize the Descriptor WB path for RS bit with the same
* algorithm.
*
* Note: If there are less than 4 packets
* pending and interrupts were disabled the service task will
* trigger a force WB.
*/
if (skb->xmit_more &&
!netif_xmit_stopped(netdev_get_tx_queue(tx_ring->netdev,
tx_ring->queue_index))) {
tx_ring->flags |= I40E_TXR_FLAGS_LAST_XMIT_MORE_SET;
tail_bump = false;
} else if (!skb->xmit_more &&
!netif_xmit_stopped(netdev_get_tx_queue(tx_ring->netdev,
tx_ring->queue_index)) &&
(!(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 {
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);
/* notify HW of packet */
if (!skb->xmit_more ||
netif_xmit_stopped(netdev_get_tx_queue(tx_ring->netdev,
tx_ring->queue_index)))
writel(i, tx_ring->tail);
else
if (!tail_bump)
prefetchw(tx_desc + 1);
if (tail_bump) {
/* 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();
writel(i, tx_ring->tail);
}
return;
dma_error:

2
drivers/net/ethernet/intel/i40e/i40e_txrx.h
View File

@ -256,10 +256,12 @@ struct i40e_ring {
bool ring_active; /* is ring online or not */
bool arm_wb; /* do something to arm write back */
u8 packet_stride;
u16 flags;
#define I40E_TXR_FLAGS_WB_ON_ITR BIT(0)
#define I40E_TXR_FLAGS_OUTER_UDP_CSUM BIT(1)
#define I40E_TXR_FLAGS_LAST_XMIT_MORE_SET BIT(2)
/* stats structs */
struct i40e_queue_stats stats;