From: Arthur Fabre <afabre@cloudflare.com>
To: Edward Cree <ecree@solarflare.com>
Cc: Solarflare linux maintainers <linux-net-drivers@solarflare.com>,
Charles McLachlan <cmclachlan@solarflare.com>,
Martin Habets <mhabets@solarflare.com>,
David Miller <davem@davemloft.net>,
Alexei Starovoitov <ast@kernel.org>,
Daniel Borkmann <daniel@iogearbox.net>,
Jakub Kicinski <jakub.kicinski@netronome.com>,
Jesper Dangaard Brouer <hawk@kernel.org>,
John Fastabend <john.fastabend@gmail.com>,
netdev <netdev@vger.kernel.org>, bpf <bpf@vger.kernel.org>,
kernel-team <kernel-team@cloudflare.com>
Subject: Re: [PATCH net-next] sfc: trace_xdp_exception on XDP failure
Date: Tue, 12 Nov 2019 14:52:26 +0000 [thread overview]
Message-ID: <CAOn4ftuyCNSehwLHTfZkNP27zbMOpBo+7j5N97J31-gxoAdYCQ@mail.gmail.com> (raw)
In-Reply-To: <6a3705cc-809d-0c7a-d39f-97d61c4ce58c@solarflare.com>
On Mon, Nov 11, 2019 at 6:01 PM Edward Cree <ecree@solarflare.com> wrote:
>
> On 11/11/2019 17:38, Arthur Fabre wrote:
> > On Mon, Nov 11, 2019 at 5:27 PM Edward Cree <ecree@solarflare.com> wrote:
> >>
> >> On 11/11/2019 10:51, Arthur Fabre wrote:
> >>> diff --git a/drivers/net/ethernet/sfc/rx.c b/drivers/net/ethernet/sfc/rx.c
> >>> index a7d9841105d8..5bfe1f6112a1 100644
> >>> --- a/drivers/net/ethernet/sfc/rx.c
> >>> +++ b/drivers/net/ethernet/sfc/rx.c
> >>> @@ -678,6 +678,7 @@ static bool efx_do_xdp(struct efx_nic *efx, struct efx_channel *channel,
> >>> "XDP is not possible with multiple receive fragments (%d)\n",
> >>> channel->rx_pkt_n_frags);
> >>> channel->n_rx_xdp_bad_drops++;
> >>> + trace_xdp_exception(efx->net_dev, xdp_prog, xdp_act);
> >>> return false;
> >>> }
> >> AIUI trace_xdp_exception() is improper here as we have not run
> >> the XDP program (and xdp_act is thus uninitialised).
> >>
> >> The other three, below, appear to be correct.
> >> -Ed
> >>
> >
> > Good point. Do you know under what conditions we'd end up with
> > "fragmented" packets? As far as I can tell this isn't IP
> > fragmentation?
>
> Fragments in this case means that the packet data are spread across
> multiple RX buffers (~= memory pages). This should only happen if
> the RX packet is too big to fit in a single buffer, and when
> enabling XDP we ensure that the MTU is small enough to prevent
> that. So in theory this can't happen if the NIC is functioning
> correctly.
>
> -Ed
Makes sense, thank you for the explanation.
next prev parent reply other threads:[~2019-11-12 14:52 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-11-11 10:51 [PATCH net-next] sfc: trace_xdp_exception on XDP failure Arthur Fabre
2019-11-11 17:27 ` Edward Cree
2019-11-11 17:38 ` Arthur Fabre
2019-11-11 18:01 ` Edward Cree
2019-11-12 14:52 ` Arthur Fabre [this message]
2019-11-12 19:37 ` kbuild test robot
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