From: Jacob Keller <jacob.e.keller@intel.com>
Date: Fri, 14 Jul 2017 09:10:13 -0400
Subject: i40e/i40evf: avoid dynamic ITR updates when polling or low packet
rate
Patch-mainline: v4.14-rc1
Git-commit: 742c9875759c1858c3312442a78a80f3e93d82c4
References: bsc#1056658 FATE#322188 bsc#1056662 FATE#322186
The dynamic ITR algorithm depends on a calculation of usecs which
assumes that the interrupts have been firing constantly at the interrupt
throttle rate. This is not guaranteed because we could have a low packet
rate, or have been polling in software.
We'll estimate whether this is the case by using jiffies to determine if
we've been too long. If the time difference of jiffies is larger we are
guaranteed to have an incorrect calculation. If the time difference of
jiffies is smaller we might have been polling some but the difference
shouldn't affect the calculation too much.
This ensures that we don't get stuck in BULK latency during certain rare
situations where we receive bursts of packets that force us into NAPI
polling.
Signed-off-by: Jacob Keller <jacob.e.keller@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Acked-by: Benjamin Poirier <bpoirier@suse.com>
---
drivers/net/ethernet/intel/i40e/i40e_txrx.c | 22 +++++++++++++++++-----
drivers/net/ethernet/intel/i40e/i40e_txrx.h | 1 +
drivers/net/ethernet/intel/i40evf/i40e_txrx.c | 22 +++++++++++++++++-----
drivers/net/ethernet/intel/i40evf/i40e_txrx.h | 1 +
4 files changed, 36 insertions(+), 10 deletions(-)
--- a/drivers/net/ethernet/intel/i40e/i40e_txrx.c
+++ b/drivers/net/ethernet/intel/i40e/i40e_txrx.c
@@ -961,11 +961,25 @@ static bool i40e_set_new_dynamic_itr(str
enum i40e_latency_range new_latency_range = rc->latency_range;
u32 new_itr = rc->itr;
int bytes_per_int;
- int usecs;
+ unsigned int usecs, estimated_usecs;
if (rc->total_packets == 0 || !rc->itr)
return false;
+ usecs = (rc->itr << 1) * ITR_COUNTDOWN_START;
+ bytes_per_int = rc->total_bytes / usecs;
+
+ /* The calculations in this algorithm depend on interrupts actually
+ * firing at the ITR rate. This may not happen if the packet rate is
+ * really low, or if we've been napi polling. Check to make sure
+ * that's not the case before we continue.
+ */
+ estimated_usecs = jiffies_to_usecs(jiffies - rc->last_itr_update);
+ if (estimated_usecs > usecs) {
+ new_latency_range = I40E_LOW_LATENCY;
+ goto reset_latency;
+ }
+
/* simple throttlerate management
* 0-10MB/s lowest (50000 ints/s)
* 10-20MB/s low (20000 ints/s)
@@ -977,9 +991,6 @@ static bool i40e_set_new_dynamic_itr(str
* are in 2 usec increments in the ITR registers, and make sure
* to use the smoothed values that the countdown timer gives us.
*/
- usecs = (rc->itr << 1) * ITR_COUNTDOWN_START;
- bytes_per_int = rc->total_bytes / usecs;
-
switch (new_latency_range) {
case I40E_LOWEST_LATENCY:
if (bytes_per_int > 10)
@@ -998,6 +1009,7 @@ static bool i40e_set_new_dynamic_itr(str
break;
}
+reset_latency:
rc->latency_range = new_latency_range;
switch (new_latency_range) {
@@ -1016,12 +1028,12 @@ static bool i40e_set_new_dynamic_itr(str
rc->total_bytes = 0;
rc->total_packets = 0;
+ rc->last_itr_update = jiffies;
if (new_itr != rc->itr) {
rc->itr = new_itr;
return true;
}
-
return false;
}
--- a/drivers/net/ethernet/intel/i40e/i40e_txrx.h
+++ b/drivers/net/ethernet/intel/i40e/i40e_txrx.h
@@ -461,6 +461,7 @@ struct i40e_ring_container {
struct i40e_ring *ring;
unsigned int total_bytes; /* total bytes processed this int */
unsigned int total_packets; /* total packets processed this int */
+ unsigned long last_itr_update; /* jiffies of last ITR update */
u16 count;
enum i40e_latency_range latency_range;
u16 itr;
--- a/drivers/net/ethernet/intel/i40evf/i40e_txrx.c
+++ b/drivers/net/ethernet/intel/i40evf/i40e_txrx.c
@@ -359,11 +359,25 @@ static bool i40e_set_new_dynamic_itr(str
enum i40e_latency_range new_latency_range = rc->latency_range;
u32 new_itr = rc->itr;
int bytes_per_int;
- int usecs;
+ unsigned int usecs, estimated_usecs;
if (rc->total_packets == 0 || !rc->itr)
return false;
+ usecs = (rc->itr << 1) * ITR_COUNTDOWN_START;
+ bytes_per_int = rc->total_bytes / usecs;
+
+ /* The calculations in this algorithm depend on interrupts actually
+ * firing at the ITR rate. This may not happen if the packet rate is
+ * really low, or if we've been napi polling. Check to make sure
+ * that's not the case before we continue.
+ */
+ estimated_usecs = jiffies_to_usecs(jiffies - rc->last_itr_update);
+ if (estimated_usecs > usecs) {
+ new_latency_range = I40E_LOW_LATENCY;
+ goto reset_latency;
+ }
+
/* simple throttlerate management
* 0-10MB/s lowest (50000 ints/s)
* 10-20MB/s low (20000 ints/s)
@@ -375,9 +389,6 @@ static bool i40e_set_new_dynamic_itr(str
* are in 2 usec increments in the ITR registers, and make sure
* to use the smoothed values that the countdown timer gives us.
*/
- usecs = (rc->itr << 1) * ITR_COUNTDOWN_START;
- bytes_per_int = rc->total_bytes / usecs;
-
switch (new_latency_range) {
case I40E_LOWEST_LATENCY:
if (bytes_per_int > 10)
@@ -396,6 +407,7 @@ static bool i40e_set_new_dynamic_itr(str
break;
}
+reset_latency:
rc->latency_range = new_latency_range;
switch (new_latency_range) {
@@ -414,12 +426,12 @@ static bool i40e_set_new_dynamic_itr(str
rc->total_bytes = 0;
rc->total_packets = 0;
+ rc->last_itr_update = jiffies;
if (new_itr != rc->itr) {
rc->itr = new_itr;
return true;
}
-
return false;
}
--- a/drivers/net/ethernet/intel/i40evf/i40e_txrx.h
+++ b/drivers/net/ethernet/intel/i40evf/i40e_txrx.h
@@ -432,6 +432,7 @@ struct i40e_ring_container {
struct i40e_ring *ring;
unsigned int total_bytes; /* total bytes processed this int */
unsigned int total_packets; /* total packets processed this int */
+ unsigned long last_itr_update; /* jiffies of last ITR update */
u16 count;
enum i40e_latency_range latency_range;
u16 itr;