fm10k: Update ITR scaling mechanism based on PCIe link speed

Red Rock Canyon's interrupt throttle timers are based on the PCIe link speed. Because of this, the value being programmed into the ITR registers must be scaled.

For the PF, this is as simple as reading the PCIe link speed and storing the result. However, in the case of SR-IOV, the VF's interrupt throttle timers are based on the link speed of the PF. However, the VF is unable to get the link speed information from its configuration space, so the PF must inform it of what scale to use.

Rather than pass this scale via mailbox message, take advantage of unused bits in the TDLEN register to pass the scale. It is the responsibility of the PF to program this for the VF while setting up the VF queues and the responsibility of the VF to get the information accordingly. This is preferable because it allows the VF to set up the interrupts properly during initialization and matches how the MAC address is passed in the TDBAL/TDBAH registers.

These changes also resolve an issue with the existing ITR scale being too restrictive. It would throttle down to 1300ints/s at 1538 byte frames. This patch modifies the algorithm to allow for a higher range of interrupts per second, from roughly 25000int/s up to 100000int/s depending on our detection of the workload.

This patch fixes a single receiving TCP_STREAM in netperf:
- Before: 450 Mbps
- After: 20,000 Mbps

Signed-off-by Jacob Keller <[email protected]>

Discovered-by Matthew Vick <[email protected]>

---
  drivers/net/ethernet/intel/fm10k/fm10k.h      |  4 ++++
  drivers/net/ethernet/intel/fm10k/fm10k_main.c | 17 +++++++++++++----
  drivers/net/ethernet/intel/fm10k/fm10k_pci.c  | 12 ++++++++++--
  drivers/net/ethernet/intel/fm10k/fm10k_pf.c   | 18 +++++++++++++++++-
  drivers/net/ethernet/intel/fm10k/fm10k_type.h |  9 +++++++++
  drivers/net/ethernet/intel/fm10k/fm10k_vf.c   | 15 +++++++++++++--
  6 files changed, 66 insertions(+), 9 deletions(-)

drivers/net/ethernet/intel/fm10k/fm10k.h +0 -0

index c8c8c5baefda..f8ff8b409df8 100644

drivers/net/ethernet/intel/fm10k/fm10k.h +3 -0

@@ -164,6 +165,9 @@ struct fm10k_ring_container {
  #define FM10K_ITR_10K		100	/* 100us */
  #define FM10K_ITR_20K		50	/* 50us */
  #define FM10K_ITR_ADAPTIVE	0x8000	/* adaptive interrupt moderation flag */
+#define FM10K_ITR_SCALE_SMALL	60	/* constant factor for small frames */
+#define FM10K_ITR_SCALE_MEDIUM	50	/* constant factor for medium frames */
+#define FM10K_ITR_SCALE_LARGE	40	/* constant factor for large frames */
 
  #define FM10K_ITR_ENABLE	(FM10K_ITR_AUTOMASK | FM10K_ITR_MASK_CLEAR)
 

drivers/net/ethernet/intel/fm10k/fm10k_main.c +3 -3

index 4eafdad318b4..b8d43964c171 100644
@@ -1369,11 +1369,20 @@ static void fm10k_update_itr(struct fm10k_ring_container *ring_container)
  	if (avg_wire_size > 3000)
  		avg_wire_size = 3000;
 
-	/* Give a little boost to mid-size frames */
-	if ((avg_wire_size > 300) && (avg_wire_size < 1200))
-		avg_wire_size /= 3;
+	/* Simple throttle rate management based on average wire size,
+	 * providing boost to small and medium packet loads. Divide the
+	 * average wire size by a constant to calculate the minimum time

drivers/net/ethernet/intel/fm10k/fm10k_main.c +0 -0

  	/* write back value and retain adaptive flag */
  	ring_container->itr = avg_wire_size | FM10K_ITR_ADAPTIVE;

drivers/net/ethernet/intel/fm10k/fm10k_pci.c +3 -0

index df9fda38bdd1..62e2d7203846 100644
@@ -532,6 +532,9 @@ static void fm10k_configure_tx_ring(struct fm10k_intfc *interface,
  	/* store tail pointer */
  	ring->tail = &interface->uc_addr[FM10K_TDT(reg_idx)];
 
+	/* store ITR scale */
+	ring->itr_scale = hw->mac.itr_scale;
+
  	/* reset ntu and ntc to place SW in sync with hardwdare */
  	ring->next_to_clean = 0;
  	ring->next_to_use = 0;

drivers/net/ethernet/intel/fm10k/fm10k_pci.c +4 -2

@@ -824,7 +830,8 @@ static irqreturn_t fm10k_msix_mbx_vf(int __always_unused irq, void *data)
 
  	/* re-enable mailbox interrupt and indicate 20us delay */
  	fm10k_write_reg(hw, FM10K_VFITR(FM10K_MBX_VECTOR),
-			FM10K_ITR_ENABLE | FM10K_MBX_INT_DELAY);
+			FM10K_ITR_ENABLE | (FM10K_MBX_INT_DELAY /
+					    hw->mac.itr_scale));
 
  	/* service upstream mailbox */
  	if (fm10k_mbx_trylock(interface)) {

@@ -1029,7 +1036,8 @@ static irqreturn_t fm10k_msix_mbx_pf(int __always_unused irq, void *data)
 
  	/* re-enable mailbox interrupt and indicate 20us delay */
  	fm10k_write_reg(hw, FM10K_ITR(FM10K_MBX_VECTOR),
-			FM10K_ITR_ENABLE | FM10K_MBX_INT_DELAY);
+			FM10K_ITR_ENABLE | (FM10K_MBX_INT_DELAY /
+					    hw->mac.itr_scale));
 
  	return IRQ_HANDLED;
  }

drivers/net/ethernet/intel/fm10k/fm10k_pf.c +17 -1

index 891e21874b2a..5d67321bd8a4 100644
@@ -144,19 +144,26 @@ static s32 fm10k_init_hw_pf(struct fm10k_hw *hw)
  				FM10K_TPH_RXCTRL_HDR_WROEN);
  	}
 
-	/* set max hold interval to align with 1.024 usec in all modes */
+	/* set max hold interval to align with 1.024 usec in all modes and
+	 * store ITR scale
+	 */
  	switch (hw->bus.speed) {
  	case fm10k_bus_speed_2500:
  		dma_ctrl = FM10K_DMA_CTRL_MAX_HOLD_1US_GEN1;
+		hw->mac.itr_scale = FM10K_TDLEN_ITR_SCALE_GEN1;
  		break;
  	case fm10k_bus_speed_5000:
  		dma_ctrl = FM10K_DMA_CTRL_MAX_HOLD_1US_GEN2;
+		hw->mac.itr_scale = FM10K_TDLEN_ITR_SCALE_GEN2;
  		break;
  	case fm10k_bus_speed_8000:
  		dma_ctrl = FM10K_DMA_CTRL_MAX_HOLD_1US_GEN3;
+		hw->mac.itr_scale = FM10K_TDLEN_ITR_SCALE_GEN3;
  		break;
  	default:
  		dma_ctrl = 0;
+		/* just in case, assume Gen3 ITR scale */
+		hw->mac.itr_scale = FM10K_TDLEN_ITR_SCALE_GEN3;
  		break;
  	}
 

@@ -910,6 +917,12 @@ static s32 fm10k_iov_assign_default_mac_vlan_pf(struct fm10k_hw *hw,
  	fm10k_write_reg(hw, FM10K_TDBAL(vf_q_idx), tdbal);
  	fm10k_write_reg(hw, FM10K_TDBAH(vf_q_idx), tdbah);
 
+	/* Provide the VF the ITR scale, using software-defined fields in TDLEN
+	 * to pass the information during VF initialization
+	 */
+	fm10k_write_reg(hw, FM10K_TDLEN(vf_q_idx), hw->mac.itr_scale <<
+						   FM10K_TDLEN_ITR_SCALE_SHIFT);
+
  err_out:
  	/* configure Queue control register */
  	txqctl = ((u32)vf_vid << FM10K_TXQCTL_VID_SHIFT) &

@@ -1042,6 +1055,9 @@ static s32 fm10k_iov_reset_resources_pf(struct fm10k_hw *hw,
  	for (i = queues_per_pool; i--;) {
  		fm10k_write_reg(hw, FM10K_TDBAL(vf_q_idx + i), tdbal);
  		fm10k_write_reg(hw, FM10K_TDBAH(vf_q_idx + i), tdbah);
+		fm10k_write_reg(hw, FM10K_TDLEN(vf_q_idx + i),
+				hw->mac.itr_scale <<
+				FM10K_TDLEN_ITR_SCALE_SHIFT);
  		fm10k_write_reg(hw, FM10K_TQMAP(qmap_idx + i), vf_q_idx + i);
  		fm10k_write_reg(hw, FM10K_RQMAP(qmap_idx + i), vf_q_idx + i);
  	}

drivers/net/ethernet/intel/fm10k/fm10k_type.h +1 -0

index 4af96686c584..b8a2e5142041 100644
@@ -271,6 +271,14 @@ struct fm10k_hw;
  #define FM10K_TDBAL(_n)		((0x40 * (_n)) + 0x8000)
  #define FM10K_TDBAH(_n)		((0x40 * (_n)) + 0x8001)
  #define FM10K_TDLEN(_n)		((0x40 * (_n)) + 0x8002)
+/* Reuse some empty space prior to VF initialization in order for the VF to

drivers/net/ethernet/intel/fm10k/fm10k_type.h +1 -0

@@ -560,6 +568,7 @@ struct fm10k_mac_info {
  	bool get_host_state;
  	bool tx_ready;
  	u32 dglort_map;
+	u8 itr_scale;
  };
 
  struct fm10k_swapi_table_info {

drivers/net/ethernet/intel/fm10k/fm10k_vf.c +6 -2

index 94f0f6a146d9..c39eea58b124 100644
@@ -28,7 +28,7 @@
  static s32 fm10k_stop_hw_vf(struct fm10k_hw *hw)
  {
  	u8 *perm_addr = hw->mac.perm_addr;
-	u32 bal = 0, bah = 0;
+	u32 bal = 0, bah = 0, tdlen;
  	s32 err;
  	u16 i;
 

@@ -48,6 +48,9 @@ static s32 fm10k_stop_hw_vf(struct fm10k_hw *hw)
  		       ((u32)perm_addr[2]);
  	}
 
+	/* Restore default itr_scale for next VF initialization */
+	tdlen = hw->mac.itr_scale << FM10K_TDLEN_ITR_SCALE_SHIFT;
+
  	/* The queues have already been disabled so we just need to
  	 * update their base address registers
  	 */

@@ -56,6 +59,7 @@ static s32 fm10k_stop_hw_vf(struct fm10k_hw *hw)
  		fm10k_write_reg(hw, FM10K_TDBAH(i), bah);
  		fm10k_write_reg(hw, FM10K_RDBAL(i), bal);
  		fm10k_write_reg(hw, FM10K_RDBAH(i), bah);
+		fm10k_write_reg(hw, FM10K_TDLEN(i), tdlen);
  	}
 
  	return 0;

@@ -124,9 +128,16 @@ static s32 fm10k_init_hw_vf(struct fm10k_hw *hw)
  	/* record maximum queue count */
  	hw->mac.max_queues = i;
 
-	/* fetch default VLAN */
+	/* fetch default VLAN and ITR scale */
  	hw->mac.default_vid = (fm10k_read_reg(hw, FM10K_TXQCTL(0)) &
  			       FM10K_TXQCTL_VID_MASK) >> FM10K_TXQCTL_VID_SHIFT;

Quoted 28 lines · Jacob Keller

Red Rock Canyon's interrupt throttle timers are based on the PCIe link speed. Because of this, the value being programmed into the ITR registers must be scaled.

For the PF, this is as simple as reading the PCIe link speed and storing the result. However, in the case of SR-IOV, the VF's interrupt throttle timers are based on the link speed of the PF. However, the VF is unable to get the link speed information from its configuration space, so the PF must inform it of what scale to use.

Rather than pass this scale via mailbox message, take advantage of unused bits in the TDLEN register to pass the scale. It is the responsibility of the PF to program this for the VF while setting up the VF queues and the responsibility of the VF to get the information accordingly. This is preferable because it allows the VF to set up the interrupts properly during initialization and matches how the MAC address is passed in the TDBAL/TDBAH registers.

These changes also resolve an issue with the existing ITR scale being too restrictive. It would throttle down to 1300ints/s at 1538 byte frames. This patch modifies the algorithm to allow for a higher range of interrupts per second, from roughly 25000int/s up to 100000int/s depending on our detection of the workload.

This patch fixes a single receiving TCP_STREAM in netperf:
- Before: 450 Mbps
- After: 20,000 Mbps

Quoted 2 lines

Signed-off-by Jacob Keller <[email protected]>

Discovered-by Matthew Vick <[email protected]>

Should probably be Reported-by, since I don't think Discovered-by is a standard convention.

Also I don't think I see any of the changes I suggested. It seems like this could still divide the interrupt throttle rate all the way down to 0.

Quoted 4 lines · Alexander Duyck

Also I don't think I see any of the changes I suggested. It seems like this could still divide the interrupt throttle rate all the way down to 0.

I'm going to defer this for a bit then, since it depends on other changes I wasn't aware of.. Matthew?

Regards,
Jake

Red Rock Canyon's interrupt throttle timers are based on the PCIe link speed. Because of this, the value being programmed into the ITR registers must be scaled.

For the PF, this is as simple as reading the PCIe link speed and storing
the result. However, in the case of SR-IOV, the VF's interrupt throttle
timers are based on the link speed of the PF. However, the VF is unable
to get the link speed information from its configuration space, so the PF must inform it of what scale to use.

Rather than pass this scale via mailbox message, take advantage of unused bits in the TDLEN register to pass the scale. It is the responsibility of the PF to program this for the VF while setting up the
VF queues and the responsibility of the VF to get the information accordingly. This is preferable because it allows the VF to set up the interrupts properly during initialization and matches how the MAC address is passed in the TDBAL/TDBAH registers.

These changes also resolve an issue with the existing ITR scale being too restrictive. It would throttle down to 1300ints/s at 1538 byte frames. This patch modifies the algorithm to allow for a higher range of
interrupts per second, from roughly 25000int/s up to 100000int/s depending on our detection of the workload.

This patch fixes a single receiving TCP_STREAM in netperf:
- Before: 450 Mbps
- After: 20,000 Mbps

Signed-off-by Jacob Keller <[email protected]>

Discovered-by Matthew Vick <[email protected]>

---
 drivers/net/ethernet/intel/fm10k/fm10k.h      |  4 ++++
 drivers/net/ethernet/intel/fm10k/fm10k_main.c | 17 +++++++++++++----
 drivers/net/ethernet/intel/fm10k/fm10k_pci.c  | 12 ++++++++++--
 drivers/net/ethernet/intel/fm10k/fm10k_pf.c   | 18 +++++++++++++++++-
 drivers/net/ethernet/intel/fm10k/fm10k_type.h |  9 +++++++++
 drivers/net/ethernet/intel/fm10k/fm10k_vf.c   | 15 +++++++++++++--
 6 files changed, 66 insertions(+), 9 deletions(-)