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Message-Id: <1449044735-68599-4-git-send-email-jeffrey.t.kirsher@intel.com>
Date: Wed, 2 Dec 2015 00:25:21 -0800
From: Jeff Kirsher <jeffrey.t.kirsher@...el.com>
To: davem@...emloft.net
Cc: Anjali Singhai Jain <anjali.singhai@...el.com>,
netdev@...r.kernel.org, nhorman@...hat.com, sassmann@...hat.com,
jogreene@...hat.com, Jeff Kirsher <jeffrey.t.kirsher@...el.com>
Subject: [net-next 03/17] i40e/i40evf: Fix RS bit update in Tx path and disable force WB workaround
From: Anjali Singhai Jain <anjali.singhai@...el.com>
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 amd when
it does a WB. It also optimizes when we do a wmb.
Change-ID: Id831e1ae7d3e2ec3f52cd0917b41ce1d22d75d9d
Signed-off-by: Anjali Singhai Jain <anjali.singhai@...el.com>
Tested-by: Andrew Bowers <andrewx.bowers@...el.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@...el.com>
---
drivers/net/ethernet/intel/i40evf/i40e_txrx.c | 118 ++++++++++++++++----------
drivers/net/ethernet/intel/i40evf/i40e_txrx.h | 2 +
2 files changed, 77 insertions(+), 43 deletions(-)
diff --git a/drivers/net/ethernet/intel/i40evf/i40e_txrx.c b/drivers/net/ethernet/intel/i40evf/i40e_txrx.c
index 8629a9f..23fd112 100644
--- a/drivers/net/ethernet/intel/i40evf/i40e_txrx.c
+++ b/drivers/net/ethernet/intel/i40evf/i40e_txrx.c
@@ -245,16 +245,6 @@ 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;
-
netdev_tx_completed_queue(netdev_get_tx_queue(tx_ring->netdev,
tx_ring->queue_index),
total_packets, total_bytes);
@@ -1770,6 +1760,9 @@ 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;
if (tx_flags & I40E_TX_FLAGS_HW_VLAN) {
td_cmd |= I40E_TX_DESC_CMD_IL2TAG1;
@@ -1810,6 +1803,8 @@ static inline void i40evf_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;
@@ -1829,6 +1824,8 @@ static inline void i40evf_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;
@@ -1843,35 +1840,7 @@ static inline void i40evf_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.
- */
#define WB_STRIDE 0x3
- 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;
@@ -1881,15 +1850,78 @@ 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(netdev_get_tx_queue(tx_ring->netdev,
+ tx_ring->queue_index),
+ first->bytecount);
i40evf_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.
+ * else (kernel < 3.18)
+ * if every packet spanned less than 4 desc
+ * then set RS bit on 4th packet and update tail
+ * on every packet
+ * else
+ * set RS bit on EOP for every packet and update tail
+ *
+ * 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:
diff --git a/drivers/net/ethernet/intel/i40evf/i40e_txrx.h b/drivers/net/ethernet/intel/i40evf/i40e_txrx.h
index 997b374..929ddd9 100644
--- a/drivers/net/ethernet/intel/i40evf/i40e_txrx.h
+++ b/drivers/net/ethernet/intel/i40evf/i40e_txrx.h
@@ -268,6 +268,8 @@ 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)
--
2.5.0
--
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