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Message-ID: <Z6IJppEFhSzMbmi9@boxer>
Date: Tue, 4 Feb 2025 13:35:50 +0100
From: Maciej Fijalkowski <maciej.fijalkowski@...el.com>
To: "Song, Yoong Siang" <yoong.siang.song@...el.com>
CC: "David S . Miller" <davem@...emloft.net>, Eric Dumazet
<edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni
<pabeni@...hat.com>, Simon Horman <horms@...nel.org>, Willem de Bruijn
<willemb@...gle.com>, "Bezdeka, Florian" <florian.bezdeka@...mens.com>,
Donald Hunter <donald.hunter@...il.com>, Jonathan Corbet <corbet@....net>,
Bjorn Topel <bjorn@...nel.org>, "Karlsson, Magnus"
<magnus.karlsson@...el.com>, Jonathan Lemon <jonathan.lemon@...il.com>,
Andrew Lunn <andrew+netdev@...n.ch>, Alexei Starovoitov <ast@...nel.org>,
Daniel Borkmann <daniel@...earbox.net>, Jesper Dangaard Brouer
<hawk@...nel.org>, John Fastabend <john.fastabend@...il.com>, "Damato, Joe"
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Jurgens" <danielj@...dia.com>, Andrii Nakryiko <andrii@...nel.org>, "Eduard
Zingerman" <eddyz87@...il.com>, Mykola Lysenko <mykolal@...com>, "Martin
KaFai Lau" <martin.lau@...ux.dev>, Song Liu <song@...nel.org>, Yonghong Song
<yonghong.song@...ux.dev>, KP Singh <kpsingh@...nel.org>, Hao Luo
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<shuah@...nel.org>, Alexandre Torgue <alexandre.torgue@...s.st.com>, "Jose
Abreu" <joabreu@...opsys.com>, Maxime Coquelin <mcoquelin.stm32@...il.com>,
"Nguyen, Anthony L" <anthony.l.nguyen@...el.com>, "Kitszel, Przemyslaw"
<przemyslaw.kitszel@...el.com>, Faizal Rahim
<faizal.abdul.rahim@...ux.intel.com>, Choong Yong Liang
<yong.liang.choong@...ux.intel.com>, "Bouska, Zdenek"
<zdenek.bouska@...mens.com>, "netdev@...r.kernel.org"
<netdev@...r.kernel.org>, "linux-kernel@...r.kernel.org"
<linux-kernel@...r.kernel.org>, "linux-doc@...r.kernel.org"
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<linux-arm-kernel@...ts.infradead.org>, "intel-wired-lan@...ts.osuosl.org"
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<xdp-hints@...-project.net>
Subject: Re: [PATCH bpf-next v7 4/5] igc: Refactor empty packet insertion
into a reusable function
On Tue, Feb 04, 2025 at 12:07:21PM +0100, Song, Yoong Siang wrote:
> On Tuesday, February 4, 2025 5:50 PM, Fijalkowski, Maciej <maciej.fijalkowski@...el.com> wrote:
> >On Tue, Feb 04, 2025 at 08:49:06AM +0800, Song Yoong Siang wrote:
> >> Refactor the code for inserting an empty packet into a new function
> >> igc_insert_empty_packet(). This change extracts the logic for inserting
> >> an empty packet from igc_xmit_frame_ring() into a separate function,
> >> allowing it to be reused in future implementations, such as the XDP
> >> zero copy transmit function.
> >>
> >> This patch introduces no functional changes.
> >>
> >> Signed-off-by: Song Yoong Siang <yoong.siang.song@...el.com>
> >> ---
> >> drivers/net/ethernet/intel/igc/igc_main.c | 42 ++++++++++++-----------
> >> 1 file changed, 22 insertions(+), 20 deletions(-)
> >>
> >> diff --git a/drivers/net/ethernet/intel/igc/igc_main.c
> >b/drivers/net/ethernet/intel/igc/igc_main.c
> >> index 56a35d58e7a6..c3edd8bcf633 100644
> >> --- a/drivers/net/ethernet/intel/igc/igc_main.c
> >> +++ b/drivers/net/ethernet/intel/igc/igc_main.c
> >> @@ -1566,6 +1566,26 @@ static bool igc_request_tx_tstamp(struct igc_adapter
> >*adapter, struct sk_buff *s
> >> return false;
> >> }
> >>
> >> +static void igc_insert_empty_packet(struct igc_ring *tx_ring)
> >> +{
> >> + struct igc_tx_buffer *empty_info;
> >> + struct sk_buff *empty;
> >> + void *data;
> >> +
> >> + empty_info = &tx_ring->tx_buffer_info[tx_ring->next_to_use];
> >> + empty = alloc_skb(IGC_EMPTY_FRAME_SIZE, GFP_ATOMIC);
> >> + if (!empty)
> >> + return;
> >> +
> >> + data = skb_put(empty, IGC_EMPTY_FRAME_SIZE);
> >> + memset(data, 0, IGC_EMPTY_FRAME_SIZE);
> >> +
> >> + igc_tx_ctxtdesc(tx_ring, 0, false, 0, 0, 0);
> >> +
> >> + if (igc_init_tx_empty_descriptor(tx_ring, empty, empty_info) < 0)
> >> + dev_kfree_skb_any(empty);
> >> +}
> >> +
> >> static netdev_tx_t igc_xmit_frame_ring(struct sk_buff *skb,
> >> struct igc_ring *tx_ring)
> >> {
> >> @@ -1603,26 +1623,8 @@ static netdev_tx_t igc_xmit_frame_ring(struct
> >sk_buff *skb,
> >> skb->tstamp = ktime_set(0, 0);
> >> launch_time = igc_tx_launchtime(tx_ring, txtime, &first_flag,
> >&insert_empty);
> >>
> >> - if (insert_empty) {
> >> - struct igc_tx_buffer *empty_info;
> >> - struct sk_buff *empty;
> >> - void *data;
> >> -
> >> - empty_info = &tx_ring->tx_buffer_info[tx_ring->next_to_use];
> >> - empty = alloc_skb(IGC_EMPTY_FRAME_SIZE, GFP_ATOMIC);
> >> - if (!empty)
> >> - goto done;
> >
> >shouldn't this be 'goto drop' from day 1? pretty weird to silently ignore
> >allocation error.
> >
>
> Hi Fijalkowski Maciej,
>
> Thanks for your comments.
>
> "insert an empty packet" is a launch time trick to send a packet in
> next Qbv cycle. The design is, the driver will still sending the
> packet, even the empty packet insertion trick is fail (unable to
> allocate). The intention of this patch set is to enable launch time
> on XDP zero-copy data path, so I try not to change the original
> behavior of launch time.
>
> btw, do you think driver should drop the packet if something went
> wrong with the launch time, like launch time offload not enabled,
> launch time over horizon, empty packet insertion fail, etc?
> If yes, then maybe i can submit another patch to change the behavior
> of launch time and we can continue to discuss there.
That's rather a question to you since I am no TSN expert here :P
the alloc skbs failures would rather be a minor thing but anyways it
didn't look correct from a first glance to silently ignore this behavior
if rest of the logic relies on this. I won't be insisting on any changes
here but it's something you could consider to change maybe.
The real question is in 5/5, regarding the cleaning of these empty descs
from ZC path.
>
> >> -
> >> - data = skb_put(empty, IGC_EMPTY_FRAME_SIZE);
> >> - memset(data, 0, IGC_EMPTY_FRAME_SIZE);
> >> -
> >> - igc_tx_ctxtdesc(tx_ring, 0, false, 0, 0, 0);
> >> -
> >> - if (igc_init_tx_empty_descriptor(tx_ring,
> >> - empty,
> >> - empty_info) < 0)
> >> - dev_kfree_skb_any(empty);
> >
> >ditto
> >
>
> ditto
>
> >> - }
> >> + if (insert_empty)
> >> + igc_insert_empty_packet(tx_ring);
> >>
> >> done:
> >> /* record the location of the first descriptor for this packet */
> >> --
> >> 2.34.1
> >>
>
> Thanks & Regards
> Siang
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