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From: Edward Cree <ecree@solarflare.com>
To: Arthur Fabre <afabre@cloudflare.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: Mon, 11 Nov 2019 18:01:30 +0000	[thread overview]
Message-ID: <6a3705cc-809d-0c7a-d39f-97d61c4ce58c@solarflare.com> (raw)
In-Reply-To: <CAOn4ftvqib3y+Gfhq+dS4cUeWQVyGDM+rNeLnoVoYz9O_VLYLA@mail.gmail.com>

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


  reply	other threads:[~2019-11-11 18:01 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 [this message]
2019-11-12 14:52       ` Arthur Fabre
2019-11-12 19:37 ` kbuild test robot

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