On Sat, Nov 10, 2018 at 6:31 AM Björn Töpel <bjorn.topel@xxxxxxxxx> wrote:
>
> Den tors 8 nov. 2018 kl 16:15 skrev Konrad Djimeli <kdjimeli@xxxxxxxxxx>:
> >
> [...]
> > > In terms of correctness:
> > >
> > > In 3. you pass the same UMEM indicies to the Tx ring (ids={0,
> > > FRAME_SIZE, 2*FRAME_SIZE, ...}), as you have passed to the fill
> > > ring. This is not correct. Userspace to track what ids are owned by
> > > the user and by the kernel. Now, both the fill ring and Tx ring
> > > contain the same id.
> > Please I have been looking into this for some days now, but I have not
> > been able to understand what you where referring to and how to fix it.
> >
>
> Ok, let's talk about the basics, and hopefully it will clear up. The
> indicies/ids into the UMEM are used to point out packet buffers.
>
> The Rx/Tx/Completion/Fill rings are used to pass ownership between the
> kernel and the user application. E.g. if fill id X with data and pass
> that to the kernel for transmission, the application has passed
> ownership of buffer X to the kernel. The application cannot (well,
> shouldn't) touch the buffer pointed out by X until the kernel is done
> with the buffer -- in other words, when the buffer is passed back to
> the application via the completion ring. Analogous, when you pass id Y
> to the fill ring, Y is owned by the kernel. The application cannot
> (again, shouldn't) touch the data pointed out by Y until ownership is
> passed back to the application via the Rx ring.
>
Hi Konrad,
I made a slide about using how the rx/tx/completion/fill ring works for OVS.
Hope this is helpful for you.
https://drive.google.com/open?id=1gM3lndS6WeS16QNk74L22UNx5D5wlS2o
Another thing for debugging is first to add a print in the XDP code,
so making sure the packet is there at the XDP layer.
https://github.com/williamtu/ovs-ebpf/blob/afxdp-array/bpf/xdp.h#L71
Then I usually prints the xsk stats
https://github.com/williamtu/ovs-ebpf/blob/afxdp-array/lib/netdev-linux.c#L656
So making sure I'm not mess up with these rings.
Regards,
William
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