On Thu, 6 Jun 2019 20:04:20 +0900
Toshiaki Makita <toshiaki.makita1@xxxxxxxxx> wrote:
> On 2019/06/05 16:59, Jesper Dangaard Brouer wrote:
> > On Wed, 5 Jun 2019 14:36:12 +0900
> > Toshiaki Makita <toshiaki.makita1@xxxxxxxxx> wrote:
> >
> >> This is introduced for admins to check what is happening on XDP_TX when
> >> bulk XDP_TX is in use, which will be first introduced in veth in next
> >> commit.
> >
> > Is the plan that this tracepoint 'xdp:xdp_bulk_tx' should be used by
> > all drivers?
>
> I guess you mean all drivers that implement similar mechanism should use
> this? Then yes.
> (I don't think all drivers needs bulk tx mechanism though)
>
> > (more below)
> >
> >> Signed-off-by: Toshiaki Makita <toshiaki.makita1@xxxxxxxxx>
> >> ---
> >> include/trace/events/xdp.h | 25 +++++++++++++++++++++++++
> >> kernel/bpf/core.c | 1 +
> >> 2 files changed, 26 insertions(+)
> >>
> >> diff --git a/include/trace/events/xdp.h b/include/trace/events/xdp.h
> >> index e95cb86..e06ea65 100644
> >> --- a/include/trace/events/xdp.h
> >> +++ b/include/trace/events/xdp.h
> >> @@ -50,6 +50,31 @@
> >> __entry->ifindex)
> >> );
> >>
> >> +TRACE_EVENT(xdp_bulk_tx,
> >> +
> >> + TP_PROTO(const struct net_device *dev,
> >> + int sent, int drops, int err),
> >> +
> >> + TP_ARGS(dev, sent, drops, err),
> >> +
> >> + TP_STRUCT__entry(
> >
> > All other tracepoints in this file starts with:
> >
> > __field(int, prog_id)
> > __field(u32, act)
> > or
> > __field(int, map_id)
> > __field(u32, act)
> >
> > Could you please add those?
>
> So... prog_id is the problem. The program can be changed while we are
> enqueueing packets to the bulk queue, so the prog_id at flush may be an
> unexpected one.
Hmmm... that sounds problematic, if the XDP bpf_prog for veth can
change underneath, before the flush. Our redirect system, depend on
things being stable until the xdp_do_flush_map() operation, as will
e.g. set per-CPU (bpf_redirect_info) map_to_flush pointer (which depend
on XDP prog), and expect it to be correct/valid.
> It can be fixed by disabling NAPI when changing XDP programs. This stops
> packet processing while changing XDP programs, but I guess it is an
> acceptable compromise. Having said that, I'm honestly not so eager to
> make this change, since this will require refurbishment of one of the
> most delicate part of veth XDP, NAPI disabling/enabling mechanism.
>
> WDYT?
Sound like a bug, if XDP bpf_prog is not stable within the NAPI poll...
> >> + __field(int, ifindex)
> >> + __field(int, drops)
> >> + __field(int, sent)
> >> + __field(int, err)
> >> + ),
> >
> > The reason is that this make is easier to attach to multiple
> > tracepoints, and extract the same value.
> >
> > Example with bpftrace oneliner:
> >
> > $ sudo bpftrace -e 'tracepoint:xdp:xdp_* { @action[args->act] = count(); }'
--
Best regards,
Jesper Dangaard Brouer
MSc.CS, Principal Kernel Engineer at Red Hat
LinkedIn: http://www.linkedin.com/in/brouer
