• Alexander Duyck's avatar
    ixgbe: Limit lowest interrupt rate for adaptive interrupt moderation to 12K · 8ac34f10
    Alexander Duyck authored
    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: default avatarAlexander Duyck <alexander.h.duyck@redhat.com>
    Tested-by: default avatarKrishneil Singh <krishneil.k.singh@intel.com>
    Signed-off-by: default avatarJeff Kirsher <jeffrey.t.kirsher@intel.com>
    8ac34f10
ixgbe.h 29.1 KB