ixgbe: Limit lowest interrupt rate for adaptive interrupt moderation to 12K

This patch updates the lowest limit for adaptive interrupt interrupt
moderation to roughly 12K interrupts per second.

The way I came about reaching 12K as the desired interrupt rate is by
testing with UDP flows.  Specifically I had a simple test that ran a
netperf UDP_STREAM test at varying sizes.  What I found was as the packet
sizes increased the performance fell steadily behind until we were only
able to receive at ~4Gb/s with a message size of 65507.  A bit of digging
found that we were dropping packets for the socket in the network stack,
and looking at things further what I found was I could solve it by increasing
the interrupt rate, or increasing the rmem_default/rmem_max.  What I found was
that when the interrupt coalescing resulted in more data being processed
per interrupt than could be stored in the socket buffer we started losing
packets and the performance dropped.  So I reached 12K based on the
following math.

rmem_default = 212992
skb->truesize = 2994
212992 / 2994 = 71.14 packets to fill the buffer

packet rate at 1514 packet size is 812744pps
71.14 / 812744 = 87.9us to fill socket buffer

From there it was just a matter of choosing the interrupt rate and
providing a bit of wiggle room which is why I decided to go with 12K
interrupts per second as that uses a value of 84us.

The data below is based on VM to VM over a direct assigned ixgbe interface.
The test run was:
	netperf -H <ip> -t UDP_STREAM"

Socket  Message  Elapsed      Messages                   CPU      Service
Size    Size     Time         Okay Errors   Throughput   Util     Demand
bytes   bytes    secs            #      #   10^6bits/sec % SS     us/KB
Before:
212992   65507   60.00     1100662      0     9613.4     10.89    0.557
212992           60.00      473474            4135.4     11.27    0.576

After:
212992   65507   60.00     1100413      0     9611.2     10.73    0.549
212992           60.00      974132            8508.3     11.69    0.598

Using bare metal the data is similar but not as dramatic as the throughput
increases from about 8.5Gb/s to 9.5Gb/s.

Signed-off-by: Alexander Duyck <alexander.h.duyck@redhat.com>
Tested-by: Krishneil Singh <krishneil.k.singh@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>

diff --git a/drivers/net/ethernet/intel/ixgbe/ixgbe.h b/drivers/net/ethernet/intel/ixgbe/ixgbe.h
index edf1fb91320967f98cdc3ba56a4ad984a48b1063..a699c991ad2cfe50af67c5249f799d4cfbf87ea6 100644 (file)
--- a/drivers/net/ethernet/intel/ixgbe/ixgbe.h
+++ b/drivers/net/ethernet/intel/ixgbe/ixgbe.h
@@ -539,8 +539,7 @@ struct hwmon_buff {
 #define IXGBE_MIN_RSC_ITR      24
 #define IXGBE_100K_ITR         40
 #define IXGBE_20K_ITR          200
-#define IXGBE_10K_ITR          400
-#define IXGBE_8K_ITR           500
+#define IXGBE_12K_ITR          336
 
 /* ixgbe_test_staterr - tests bits in Rx descriptor status and error fields */
 static inline __le32 ixgbe_test_staterr(union ixgbe_adv_rx_desc *rx_desc,

diff --git a/drivers/net/ethernet/intel/ixgbe/ixgbe_ethtool.c b/drivers/net/ethernet/intel/ixgbe/ixgbe_ethtool.c
index ab2edc8e7703f014e0dc09f8d91de5dee1054083..94c4912b23308c5bbd0648d8b21a5bcaea9077aa 100644 (file)
--- a/drivers/net/ethernet/intel/ixgbe/ixgbe_ethtool.c
+++ b/drivers/net/ethernet/intel/ixgbe/ixgbe_ethtool.c
@@ -2286,7 +2286,7 @@ static int ixgbe_set_coalesce(struct net_device *netdev,
                adapter->tx_itr_setting = ec->tx_coalesce_usecs;
 
        if (adapter->tx_itr_setting == 1)
-               tx_itr_param = IXGBE_10K_ITR;
+               tx_itr_param = IXGBE_12K_ITR;
        else
                tx_itr_param = adapter->tx_itr_setting;
 

diff --git a/drivers/net/ethernet/intel/ixgbe/ixgbe_lib.c b/drivers/net/ethernet/intel/ixgbe/ixgbe_lib.c
index 68e1e757ecefce38e456c5cf2ae017ddea2ed054..f3168bcc7d87905b2f3563ea64c0fbfeda01d1d4 100644 (file)
--- a/drivers/net/ethernet/intel/ixgbe/ixgbe_lib.c
+++ b/drivers/net/ethernet/intel/ixgbe/ixgbe_lib.c
@@ -866,7 +866,7 @@ static int ixgbe_alloc_q_vector(struct ixgbe_adapter *adapter,
        if (txr_count && !rxr_count) {
                /* tx only vector */
                if (adapter->tx_itr_setting == 1)
-                       q_vector->itr = IXGBE_10K_ITR;
+                       q_vector->itr = IXGBE_12K_ITR;
                else
                        q_vector->itr = adapter->tx_itr_setting;
        } else {

diff --git a/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c b/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c
index c04480ed905ea3b1ab0cfe1d2ba94b4623d08107..acb1b91408ec4ff1fba129b37ea5e98ceed22b11 100644 (file)
--- a/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c
+++ b/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c
@@ -2261,7 +2261,7 @@ static void ixgbe_update_itr(struct ixgbe_q_vector *q_vector,
        /* simple throttlerate management
         *   0-10MB/s   lowest (100000 ints/s)
         *  10-20MB/s   low    (20000 ints/s)
-        *  20-1249MB/s bulk   (8000 ints/s)
+        *  20-1249MB/s bulk   (12000 ints/s)
         */
        /* what was last interrupt timeslice? */
        timepassed_us = q_vector->itr >> 2;
@@ -2350,7 +2350,7 @@ static void ixgbe_set_itr(struct ixgbe_q_vector *q_vector)
                new_itr = IXGBE_20K_ITR;
                break;
        case bulk_latency:
-               new_itr = IXGBE_8K_ITR;
+               new_itr = IXGBE_12K_ITR;
                break;
        default:
                break;