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Date: Thu, 23 Jul 2015 23:35:59 +0300
From: Amir Vadai <amirv@...lanox.com>
To: "David S. Miller" <davem@...emloft.net>
Cc: netdev@...r.kernel.org, Amir Vadai <amirv@...lanox.com>,
Achiad Shochat <achiad@...lanox.com>,
Or Gerlitz <ogerlitz@...lanox.com>,
Tal Alon <talal@...lanox.com>
Subject: [PATCH net-next 4/6] net/mlx5e: TX latency optimization to save DMA reads
From: Achiad Shochat <achiad@...lanox.com>
A regular TX WQE execution involves two or more DMA reads -
one to fetch the WQE, and another one per WQE gather entry.
These DMA reads obviously increase the TX latency.
There are two mlx5 mechanisms to bypass these DMA reads:
1) Inline WQE
2) Blue Flame (BF)
An inline WQE contains a whole packet, thus saves the DMA read/s
of the regular WQE gather entry/s. Inline WQE support was already
added in the previous commit.
A BF WQE is written directly to the device I/O mapped memory, thus
enables saving the DMA read that fetches the WQE.
The BF WQE I/O write must be in cache line granularity, thus uses
the CPU write combining mechanism.
A BF WQE I/O write acts also as a TX doorbell for notifying the
device of new TX WQEs.
A BF WQE is written to the same I/O mapped address as the regular TX
doorbell, thus this address is being mapped twice - once by ioremap()
and once by io_mapping_map_wc().
While both mechanisms reduce the TX latency, they both consume more CPU
cycles than a regular WQE:
- A BF WQE must still be written to host memory, in addition to being
written directly to the device I/O mapped memory.
- An inline WQE involves copying the SKB data into it.
To handle this tradeoff, we introduce here a heuristic algorithm that
strives to avoid using these two mechanisms in case the TX queue is
being back-pressured by the device, and limit their usage rate otherwise.
An inline WQE will always be "Blue Flamed" (written directly to the
device I/O mapped memory) while a BF WQE may not be inlined (may contain
gather entries).
Preliminary testing using netperf UDP_RR shows that the latency goes down
from 17.5us to 16.9us, while the message rate (tested with pktgen) stays
the same.
Signed-off-by: Achiad Shochat <achiad@...lanox.com>
Signed-off-by: Amir Vadai <amirv@...lanox.com>
---
drivers/net/ethernet/mellanox/mlx5/core/en.h | 24 +++++++++++++++------
drivers/net/ethernet/mellanox/mlx5/core/en_main.c | 12 ++++++-----
drivers/net/ethernet/mellanox/mlx5/core/en_tx.c | 26 ++++++++++++++++++-----
drivers/net/ethernet/mellanox/mlx5/core/main.c | 26 +++++++++++++++++++++--
drivers/net/ethernet/mellanox/mlx5/core/uar.c | 6 ++++++
include/linux/mlx5/driver.h | 4 +++-
6 files changed, 79 insertions(+), 19 deletions(-)
diff --git a/drivers/net/ethernet/mellanox/mlx5/core/en.h b/drivers/net/ethernet/mellanox/mlx5/core/en.h
index d9dc506..b66edd2 100644
--- a/drivers/net/ethernet/mellanox/mlx5/core/en.h
+++ b/drivers/net/ethernet/mellanox/mlx5/core/en.h
@@ -60,6 +60,7 @@
#define MLX5E_TX_CQ_POLL_BUDGET 128
#define MLX5E_UPDATE_STATS_INTERVAL 200 /* msecs */
+#define MLX5E_SQ_BF_BUDGET 16
static const char vport_strings[][ETH_GSTRING_LEN] = {
/* vport statistics */
@@ -268,7 +269,9 @@ struct mlx5e_sq {
/* dirtied @xmit */
u16 pc ____cacheline_aligned_in_smp;
u32 dma_fifo_pc;
- u32 bf_offset;
+ u16 bf_offset;
+ u16 prev_cc;
+ u8 bf_budget;
struct mlx5e_sq_stats stats;
struct mlx5e_cq cq;
@@ -281,9 +284,10 @@ struct mlx5e_sq {
struct mlx5_wq_cyc wq;
u32 dma_fifo_mask;
void __iomem *uar_map;
+ void __iomem *uar_bf_map;
struct netdev_queue *txq;
u32 sqn;
- u32 bf_buf_size;
+ u16 bf_buf_size;
u16 max_inline;
u16 edge;
struct device *pdev;
@@ -493,8 +497,10 @@ int mlx5e_update_priv_params(struct mlx5e_priv *priv,
struct mlx5e_params *new_params);
static inline void mlx5e_tx_notify_hw(struct mlx5e_sq *sq,
- struct mlx5e_tx_wqe *wqe)
+ struct mlx5e_tx_wqe *wqe, int bf_sz)
{
+ u16 ofst = MLX5_BF_OFFSET + sq->bf_offset;
+
/* ensure wqe is visible to device before updating doorbell record */
dma_wmb();
@@ -505,9 +511,15 @@ static inline void mlx5e_tx_notify_hw(struct mlx5e_sq *sq,
*/
wmb();
- mlx5_write64((__be32 *)&wqe->ctrl,
- sq->uar_map + MLX5_BF_OFFSET + sq->bf_offset,
- NULL);
+ if (bf_sz) {
+ __iowrite64_copy(sq->uar_bf_map + ofst, &wqe->ctrl, bf_sz);
+
+ /* flush the write-combining mapped buffer */
+ wmb();
+
+ } else {
+ mlx5_write64((__be32 *)&wqe->ctrl, sq->uar_map + ofst, NULL);
+ }
sq->bf_offset ^= sq->bf_buf_size;
}
diff --git a/drivers/net/ethernet/mellanox/mlx5/core/en_main.c b/drivers/net/ethernet/mellanox/mlx5/core/en_main.c
index c55fad4..4a87e9d 100644
--- a/drivers/net/ethernet/mellanox/mlx5/core/en_main.c
+++ b/drivers/net/ethernet/mellanox/mlx5/core/en_main.c
@@ -514,6 +514,7 @@ static int mlx5e_create_sq(struct mlx5e_channel *c,
sq->wq.db = &sq->wq.db[MLX5_SND_DBR];
sq->uar_map = sq->uar.map;
+ sq->uar_bf_map = sq->uar.bf_map;
sq->bf_buf_size = (1 << MLX5_CAP_GEN(mdev, log_bf_reg_size)) / 2;
sq->max_inline = param->max_inline;
@@ -524,11 +525,12 @@ static int mlx5e_create_sq(struct mlx5e_channel *c,
txq_ix = c->ix + tc * priv->params.num_channels;
sq->txq = netdev_get_tx_queue(priv->netdev, txq_ix);
- sq->pdev = c->pdev;
- sq->mkey_be = c->mkey_be;
- sq->channel = c;
- sq->tc = tc;
- sq->edge = (sq->wq.sz_m1 + 1) - MLX5_SEND_WQE_MAX_WQEBBS;
+ sq->pdev = c->pdev;
+ sq->mkey_be = c->mkey_be;
+ sq->channel = c;
+ sq->tc = tc;
+ sq->edge = (sq->wq.sz_m1 + 1) - MLX5_SEND_WQE_MAX_WQEBBS;
+ sq->bf_budget = MLX5E_SQ_BF_BUDGET;
priv->txq_to_sq_map[txq_ix] = sq;
return 0;
diff --git a/drivers/net/ethernet/mellanox/mlx5/core/en_tx.c b/drivers/net/ethernet/mellanox/mlx5/core/en_tx.c
index 351ac69..64380bc 100644
--- a/drivers/net/ethernet/mellanox/mlx5/core/en_tx.c
+++ b/drivers/net/ethernet/mellanox/mlx5/core/en_tx.c
@@ -57,7 +57,7 @@ void mlx5e_send_nop(struct mlx5e_sq *sq, bool notify_hw)
if (notify_hw) {
cseg->fm_ce_se = MLX5_WQE_CTRL_CQ_UPDATE;
- mlx5e_tx_notify_hw(sq, wqe);
+ mlx5e_tx_notify_hw(sq, wqe, 0);
}
}
@@ -110,7 +110,7 @@ u16 mlx5e_select_queue(struct net_device *dev, struct sk_buff *skb,
}
static inline u16 mlx5e_get_inline_hdr_size(struct mlx5e_sq *sq,
- struct sk_buff *skb)
+ struct sk_buff *skb, bool bf)
{
/* Some NIC TX decisions, e.g loopback, are based on the packet
* headers and occur before the data gather.
@@ -118,7 +118,7 @@ static inline u16 mlx5e_get_inline_hdr_size(struct mlx5e_sq *sq,
*/
#define MLX5E_MIN_INLINE (ETH_HLEN + 2/*vlan tag*/)
- if (skb_headlen(skb) <= sq->max_inline)
+ if (bf && (skb_headlen(skb) <= sq->max_inline))
return skb_headlen(skb);
return MLX5E_MIN_INLINE;
@@ -137,6 +137,7 @@ static netdev_tx_t mlx5e_sq_xmit(struct mlx5e_sq *sq, struct sk_buff *skb)
u8 opcode = MLX5_OPCODE_SEND;
dma_addr_t dma_addr = 0;
+ bool bf = false;
u16 headlen;
u16 ds_cnt;
u16 ihs;
@@ -149,6 +150,11 @@ static netdev_tx_t mlx5e_sq_xmit(struct mlx5e_sq *sq, struct sk_buff *skb)
else
sq->stats.csum_offload_none++;
+ if (sq->cc != sq->prev_cc) {
+ sq->prev_cc = sq->cc;
+ sq->bf_budget = (sq->cc == sq->pc) ? MLX5E_SQ_BF_BUDGET : 0;
+ }
+
if (skb_is_gso(skb)) {
u32 payload_len;
@@ -161,7 +167,10 @@ static netdev_tx_t mlx5e_sq_xmit(struct mlx5e_sq *sq, struct sk_buff *skb)
sq->stats.tso_packets++;
sq->stats.tso_bytes += payload_len;
} else {
- ihs = mlx5e_get_inline_hdr_size(sq, skb);
+ bf = sq->bf_budget &&
+ !skb->xmit_more &&
+ !skb_shinfo(skb)->nr_frags;
+ ihs = mlx5e_get_inline_hdr_size(sq, skb, bf);
MLX5E_TX_SKB_CB(skb)->num_bytes = max_t(unsigned int, skb->len,
ETH_ZLEN);
}
@@ -233,14 +242,21 @@ static netdev_tx_t mlx5e_sq_xmit(struct mlx5e_sq *sq, struct sk_buff *skb)
}
if (!skb->xmit_more || netif_xmit_stopped(sq->txq)) {
+ int bf_sz = 0;
+
+ if (bf && sq->uar_bf_map)
+ bf_sz = MLX5E_TX_SKB_CB(skb)->num_wqebbs << 3;
+
cseg->fm_ce_se = MLX5_WQE_CTRL_CQ_UPDATE;
- mlx5e_tx_notify_hw(sq, wqe);
+ mlx5e_tx_notify_hw(sq, wqe, bf_sz);
}
/* fill sq edge with nops to avoid wqe wrap around */
while ((sq->pc & wq->sz_m1) > sq->edge)
mlx5e_send_nop(sq, false);
+ sq->bf_budget = bf ? sq->bf_budget - 1 : 0;
+
sq->stats.packets++;
return NETDEV_TX_OK;
diff --git a/drivers/net/ethernet/mellanox/mlx5/core/main.c b/drivers/net/ethernet/mellanox/mlx5/core/main.c
index c34eafb..603a8b0 100644
--- a/drivers/net/ethernet/mellanox/mlx5/core/main.c
+++ b/drivers/net/ethernet/mellanox/mlx5/core/main.c
@@ -654,6 +654,22 @@ static int mlx5_core_set_issi(struct mlx5_core_dev *dev)
}
#endif
+static int map_bf_area(struct mlx5_core_dev *dev)
+{
+ resource_size_t bf_start = pci_resource_start(dev->pdev, 0);
+ resource_size_t bf_len = pci_resource_len(dev->pdev, 0);
+
+ dev->priv.bf_mapping = io_mapping_create_wc(bf_start, bf_len);
+
+ return dev->priv.bf_mapping ? 0 : -ENOMEM;
+}
+
+static void unmap_bf_area(struct mlx5_core_dev *dev)
+{
+ if (dev->priv.bf_mapping)
+ io_mapping_free(dev->priv.bf_mapping);
+}
+
static int mlx5_dev_init(struct mlx5_core_dev *dev, struct pci_dev *pdev)
{
struct mlx5_priv *priv = &dev->priv;
@@ -808,10 +824,13 @@ static int mlx5_dev_init(struct mlx5_core_dev *dev, struct pci_dev *pdev)
goto err_stop_eqs;
}
+ if (map_bf_area(dev))
+ dev_err(&pdev->dev, "Failed to map blue flame area\n");
+
err = mlx5_irq_set_affinity_hints(dev);
if (err) {
dev_err(&pdev->dev, "Failed to alloc affinity hint cpumask\n");
- goto err_free_comp_eqs;
+ goto err_unmap_bf_area;
}
MLX5_INIT_DOORBELL_LOCK(&priv->cq_uar_lock);
@@ -823,7 +842,9 @@ static int mlx5_dev_init(struct mlx5_core_dev *dev, struct pci_dev *pdev)
return 0;
-err_free_comp_eqs:
+err_unmap_bf_area:
+ unmap_bf_area(dev);
+
free_comp_eqs(dev);
err_stop_eqs:
@@ -881,6 +902,7 @@ static void mlx5_dev_cleanup(struct mlx5_core_dev *dev)
mlx5_cleanup_qp_table(dev);
mlx5_cleanup_cq_table(dev);
mlx5_irq_clear_affinity_hints(dev);
+ unmap_bf_area(dev);
free_comp_eqs(dev);
mlx5_stop_eqs(dev);
mlx5_free_uuars(dev, &priv->uuari);
diff --git a/drivers/net/ethernet/mellanox/mlx5/core/uar.c b/drivers/net/ethernet/mellanox/mlx5/core/uar.c
index 9ef8587..eb05c84 100644
--- a/drivers/net/ethernet/mellanox/mlx5/core/uar.c
+++ b/drivers/net/ethernet/mellanox/mlx5/core/uar.c
@@ -32,6 +32,7 @@
#include <linux/kernel.h>
#include <linux/module.h>
+#include <linux/io-mapping.h>
#include <linux/mlx5/driver.h>
#include <linux/mlx5/cmd.h>
#include "mlx5_core.h"
@@ -246,6 +247,10 @@ int mlx5_alloc_map_uar(struct mlx5_core_dev *mdev, struct mlx5_uar *uar)
goto err_free_uar;
}
+ if (mdev->priv.bf_mapping)
+ uar->bf_map = io_mapping_map_wc(mdev->priv.bf_mapping,
+ uar->index << PAGE_SHIFT);
+
return 0;
err_free_uar:
@@ -257,6 +262,7 @@ EXPORT_SYMBOL(mlx5_alloc_map_uar);
void mlx5_unmap_free_uar(struct mlx5_core_dev *mdev, struct mlx5_uar *uar)
{
+ io_mapping_unmap(uar->bf_map);
iounmap(uar->map);
mlx5_cmd_free_uar(mdev, uar->index);
}
diff --git a/include/linux/mlx5/driver.h b/include/linux/mlx5/driver.h
index 1c0d5d0..5fe0cae 100644
--- a/include/linux/mlx5/driver.h
+++ b/include/linux/mlx5/driver.h
@@ -380,7 +380,7 @@ struct mlx5_uar {
u32 index;
struct list_head bf_list;
unsigned free_bf_bmap;
- void __iomem *wc_map;
+ void __iomem *bf_map;
void __iomem *map;
};
@@ -435,6 +435,8 @@ struct mlx5_priv {
struct mlx5_uuar_info uuari;
MLX5_DECLARE_DOORBELL_LOCK(cq_uar_lock);
+ struct io_mapping *bf_mapping;
+
/* pages stuff */
struct workqueue_struct *pg_wq;
struct rb_root page_root;
--
2.4.3.413.ga5fe668
--
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