netmap / LINUX realtime / ixgbevf: huge RX latencies

[K. Macy]

HEAD or 11?


On Thu, Nov 30, 2017 at 13:03 Joe Buehler <aspam at cox.net> wrote:

> I am using the LINUX 4.4.86 realtime kernel patch with netmap and the
> ixgbevf driver (SRIOV in a VM) and having some serious RX latency issues.
>
> The ixbgevf driver built by the netmap build against the kernel source
> does not work.  I haven't tried to debug it -- the netmap driver
> complains about bad ring index values and resets (over and over again as
> my app runs).
>
> The non-netmap version of ixgbevf that comes with the kernel works but
> appears to have serious RX latency issues due to frame batching.  It
> appears that the kernel's NAPI polling reads frames from the NIC, then
> netmap processes the frames, then epoll exits and my app can work on the
> frames.  The delay between start of NAPI to my app getting frames can be
> milliseconds!!!
>
> Would the netmap-modified ixgbevf driver eliminate this latency?
>
> If so, any ideas on what might be going wrong with the modified driver?
>  Perhaps an older version of the driver might be better?  The kernel
> ixgbevf version is 2.12.1-k while netmap is trying to use 4.2.1.
> Looking at the RT patch for LINUX there are only a few network driver
> patches, none for the ixgbe* cards.
>
> Joe Buehler
>
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