• Magnus Karlsson's avatar
    i40e: need_wakeup flag might not be set for Tx · 70563957
    Magnus Karlsson authored
    The need_wakeup flag for Tx might not be set for AF_XDP sockets that
    are only used to send packets. This happens if there is at least one
    outstanding packet that has not been completed by the hardware and we
    get that corresponding completion (which will not generate an
    interrupt since interrupts are disabled in the napi poll loop) between
    the time we stopped processing the Tx completions and interrupts are
    enabled again. In this case, the need_wakeup flag will have been
    cleared at the end of the Tx completion processing as we believe we
    will get an interrupt from the outstanding completion at a later point
    in time. But if this completion interrupt occurs before interrupts
    are enable, we lose it and should at that point really have set the
    need_wakeup flag since there are no more outstanding completions that
    can generate an interrupt to continue the processing. When this
    happens, user space will see a Tx queue need_wakeup of 0 and skip
    issuing a syscall, which means will never get into the Tx processing
    again and we have a deadlock.
    
    This patch introduces a quick fix for this issue by just setting the
    need_wakeup flag for Tx to 1 all the time. I am working on a proper
    fix for this that will toggle the flag appropriately, but it is more
    challenging than I anticipated and I am afraid that this patch will
    not be completed before the merge window closes, therefore this easier
    fix for now. This fix has a negative performance impact in the range
    of 0% to 4%. Towards the higher end of the scale if you have driver
    and application on the same core and issue a lot of packets, and
    towards no negative impact if you use two cores, lower transmission
    speeds and/or a workload that also receives packets.
    Signed-off-by: default avatarMagnus Karlsson <magnus.karlsson@intel.com>
    Tested-by: default avatarAndrew Bowers <andrewx.bowers@intel.com>
    Signed-off-by: default avatarJeff Kirsher <jeffrey.t.kirsher@intel.com>
    70563957
i40e_xsk.c 20.9 KB