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Date: Fri, 13 Jan 2023 22:31:59 +0100
From: Toke Høiland-Jørgensen <toke@...hat.com>
To: Tariq Toukan <ttoukan.linux@...il.com>,
Stanislav Fomichev <sdf@...gle.com>,
Tariq Toukan <ttoukan.linux@...il.com>
Cc: bpf@...r.kernel.org, ast@...nel.org, daniel@...earbox.net,
andrii@...nel.org, martin.lau@...ux.dev, song@...nel.org,
yhs@...com, john.fastabend@...il.com, kpsingh@...nel.org,
haoluo@...gle.com, jolsa@...nel.org,
Saeed Mahameed <saeedm@...dia.com>,
David Ahern <dsahern@...il.com>,
Jakub Kicinski <kuba@...nel.org>,
Willem de Bruijn <willemb@...gle.com>,
Jesper Dangaard Brouer <brouer@...hat.com>,
Anatoly Burakov <anatoly.burakov@...el.com>,
Alexander Lobakin <alexandr.lobakin@...el.com>,
Magnus Karlsson <magnus.karlsson@...il.com>,
Maryam Tahhan <mtahhan@...hat.com>, xdp-hints@...-project.net,
netdev@...r.kernel.org
Subject: Re: [xdp-hints] Re: [PATCH bpf-next v7 15/17] net/mlx5e: Introduce
wrapper for xdp_buff
Tariq Toukan <ttoukan.linux@...il.com> writes:
> On 12/01/2023 23:55, Toke Høiland-Jørgensen wrote:
>> Toke Høiland-Jørgensen <toke@...hat.com> writes:
>>
>>> Stanislav Fomichev <sdf@...gle.com> writes:
>>>
>>>> On Thu, Jan 12, 2023 at 12:07 AM Tariq Toukan <ttoukan.linux@...il.com> wrote:
>>>>>
>>>>>
>>>>>
>>>>> On 12/01/2023 2:32, Stanislav Fomichev wrote:
>>>>>> From: Toke Høiland-Jørgensen <toke@...hat.com>
>>>>>>
>>>>>> Preparation for implementing HW metadata kfuncs. No functional change.
>>>>>>
>>>>>> Cc: Tariq Toukan <tariqt@...dia.com>
>>>>>> Cc: Saeed Mahameed <saeedm@...dia.com>
>>>>>> Cc: John Fastabend <john.fastabend@...il.com>
>>>>>> Cc: David Ahern <dsahern@...il.com>
>>>>>> Cc: Martin KaFai Lau <martin.lau@...ux.dev>
>>>>>> Cc: Jakub Kicinski <kuba@...nel.org>
>>>>>> Cc: Willem de Bruijn <willemb@...gle.com>
>>>>>> Cc: Jesper Dangaard Brouer <brouer@...hat.com>
>>>>>> Cc: Anatoly Burakov <anatoly.burakov@...el.com>
>>>>>> Cc: Alexander Lobakin <alexandr.lobakin@...el.com>
>>>>>> Cc: Magnus Karlsson <magnus.karlsson@...il.com>
>>>>>> Cc: Maryam Tahhan <mtahhan@...hat.com>
>>>>>> Cc: xdp-hints@...-project.net
>>>>>> Cc: netdev@...r.kernel.org
>>>>>> Signed-off-by: Toke Høiland-Jørgensen <toke@...hat.com>
>>>>>> Signed-off-by: Stanislav Fomichev <sdf@...gle.com>
>>>>>> ---
>>>>>> drivers/net/ethernet/mellanox/mlx5/core/en.h | 1 +
>>>>>> .../net/ethernet/mellanox/mlx5/core/en/xdp.c | 3 +-
>>>>>> .../net/ethernet/mellanox/mlx5/core/en/xdp.h | 6 +-
>>>>>> .../ethernet/mellanox/mlx5/core/en/xsk/rx.c | 25 ++++----
>>>>>> .../net/ethernet/mellanox/mlx5/core/en_rx.c | 58 +++++++++----------
>>>>>> 5 files changed, 50 insertions(+), 43 deletions(-)
>>>>>>
>>>>>> diff --git a/drivers/net/ethernet/mellanox/mlx5/core/en.h b/drivers/net/ethernet/mellanox/mlx5/core/en.h
>>>>>> index 2d77fb8a8a01..af663978d1b4 100644
>>>>>> --- a/drivers/net/ethernet/mellanox/mlx5/core/en.h
>>>>>> +++ b/drivers/net/ethernet/mellanox/mlx5/core/en.h
>>>>>> @@ -469,6 +469,7 @@ struct mlx5e_txqsq {
>>>>>> union mlx5e_alloc_unit {
>>>>>> struct page *page;
>>>>>> struct xdp_buff *xsk;
>>>>>> + struct mlx5e_xdp_buff *mxbuf;
>>>>>
>>>>> In XSK files below you mix usage of both alloc_units[page_idx].mxbuf and
>>>>> alloc_units[page_idx].xsk, while both fields share the memory of a union.
>>>>>
>>>>> As struct mlx5e_xdp_buff wraps struct xdp_buff, I think that you just
>>>>> need to change the existing xsk field type from struct xdp_buff *xsk
>>>>> into struct mlx5e_xdp_buff *xsk and align the usage.
>>>>
>>>> Hmmm, good point. I'm actually not sure how it works currently.
>>>> mlx5e_alloc_unit.mxbuf doesn't seem to be initialized anywhere? Toke,
>>>> am I missing something?
>>>
>>> It's initialised piecemeal in different places; but yeah, we're mixing
>>> things a bit...
>>>
>>>> I'm thinking about something like this:
>>>>
>>>> diff --git a/drivers/net/ethernet/mellanox/mlx5/core/en.h
>>>> b/drivers/net/ethernet/mellanox/mlx5/core/en.h
>>>> index af663978d1b4..2d77fb8a8a01 100644
>>>> --- a/drivers/net/ethernet/mellanox/mlx5/core/en.h
>>>> +++ b/drivers/net/ethernet/mellanox/mlx5/core/en.h
>>>> @@ -469,7 +469,6 @@ struct mlx5e_txqsq {
>>>> union mlx5e_alloc_unit {
>>>> struct page *page;
>>>> struct xdp_buff *xsk;
>>>> - struct mlx5e_xdp_buff *mxbuf;
>>>> };
>>>
>>> Hmm, for consistency with the non-XSK path we should rather go the other
>>> direction and lose the xsk member, moving everything to mxbuf? Let me
>>> give that a shot...
>>
>> Something like the below?
>>
>> -Toke
>>
>> diff --git a/drivers/net/ethernet/mellanox/mlx5/core/en.h b/drivers/net/ethernet/mellanox/mlx5/core/en.h
>> index 6de02d8aeab8..cb9cdb6421c5 100644
>> --- a/drivers/net/ethernet/mellanox/mlx5/core/en.h
>> +++ b/drivers/net/ethernet/mellanox/mlx5/core/en.h
>> @@ -468,7 +468,6 @@ struct mlx5e_txqsq {
>>
>> union mlx5e_alloc_unit {
>> struct page *page;
>> - struct xdp_buff *xsk;
>> struct mlx5e_xdp_buff *mxbuf;
>> };
>>
>> diff --git a/drivers/net/ethernet/mellanox/mlx5/core/en/xdp.h b/drivers/net/ethernet/mellanox/mlx5/core/en/xdp.h
>> index cb568c62aba0..95694a25ec31 100644
>> --- a/drivers/net/ethernet/mellanox/mlx5/core/en/xdp.h
>> +++ b/drivers/net/ethernet/mellanox/mlx5/core/en/xdp.h
>> @@ -33,6 +33,7 @@
>> #define __MLX5_EN_XDP_H__
>>
>> #include <linux/indirect_call_wrapper.h>
>> +#include <net/xdp_sock_drv.h>
>>
>> #include "en.h"
>> #include "en/txrx.h"
>> @@ -112,6 +113,21 @@ static inline void mlx5e_xmit_xdp_doorbell(struct mlx5e_xdpsq *sq)
>> }
>> }
>>
>> +static inline struct mlx5e_xdp_buff *mlx5e_xsk_buff_alloc(struct xsk_buff_pool *pool)
>> +{
>> + return (struct mlx5e_xdp_buff *)xsk_buff_alloc(pool);
>
> What about the space needed for the rq / cqe fields? xsk_buff_alloc
> won't allocate it.
It will! See patch 14 in the series that adds a 'cb' field to
xdp_buff_xsk, meaning there's actually space after the xdp_buff struct
being allocated by the xsk_buff_alloc API. The XSK_CHECK_PRIV_TYPE macro
call is there to ensure the cb field is big enough for the struct we're
casting to in the driver.
>> +}
>> +
>> +static inline void mlx5e_xsk_buff_free(struct mlx5e_xdp_buff *mxbuf)
>> +{
>> + xsk_buff_free(&mxbuf->xdp);
>> +}
>> +
>> +static inline dma_addr_t mlx5e_xsk_buff_xdp_get_frame_dma(struct mlx5e_xdp_buff *mxbuf)
>> +{
>> + return xsk_buff_xdp_get_frame_dma(&mxbuf->xdp);
>> +}
>> +
>> /* Enable inline WQEs to shift some load from a congested HCA (HW) to
>> * a less congested cpu (SW).
>> */
>> diff --git a/drivers/net/ethernet/mellanox/mlx5/core/en/xsk/rx.c b/drivers/net/ethernet/mellanox/mlx5/core/en/xsk/rx.c
>> index 8bf3029abd3c..1f166dbb7f22 100644
>> --- a/drivers/net/ethernet/mellanox/mlx5/core/en/xsk/rx.c
>> +++ b/drivers/net/ethernet/mellanox/mlx5/core/en/xsk/rx.c
>> @@ -3,7 +3,6 @@
>>
>> #include "rx.h"
>> #include "en/xdp.h"
>> -#include <net/xdp_sock_drv.h>
>> #include <linux/filter.h>
>>
>> /* RX data path */
>> @@ -21,7 +20,7 @@ int mlx5e_xsk_alloc_rx_mpwqe(struct mlx5e_rq *rq, u16 ix)
>> if (unlikely(!xsk_buff_can_alloc(rq->xsk_pool, rq->mpwqe.pages_per_wqe)))
>> goto err;
>>
>> - BUILD_BUG_ON(sizeof(wi->alloc_units[0]) != sizeof(wi->alloc_units[0].xsk));
>> + BUILD_BUG_ON(sizeof(wi->alloc_units[0]) != sizeof(wi->alloc_units[0].mxbuf));
>> XSK_CHECK_PRIV_TYPE(struct mlx5e_xdp_buff);
>> batch = xsk_buff_alloc_batch(rq->xsk_pool, (struct xdp_buff **)wi->alloc_units,
>> rq->mpwqe.pages_per_wqe);
>
> This batching API gets broken as well...
> xsk_buff_alloc_batch fills an array of struct xdp_buff pointers, it
> cannot correctly act on the array of struct mlx5e_xdp_buff, as it
> contains additional fields.
See above for why this does, in fact, work. I agree it's not totally
obvious, and in any case there's going to be a point where the cast
happens where type safety will break, which is what I was alluding to in
my reply to Stanislav.
I guess we could try to rework the API in xdp_sock_drv.h to make this
more obvious instead of using the casting driver-specific wrappers I
suggested here. Or we could go with Stanislav's suggestion of keeping
allocation etc using xdp_buff and only casting to mlx5e_xdp_buff in the
function where it's used; then we can keep the casting localised to that
function, and put a comment there explaining why it works?
> Maybe letting mlx5e_xdp_buff point to its struct xdp_buff (instead of
> wrapping it) will solve the problems here, then we'll loop over the
> xdp_buff * array and copy the pointers into the struct mlx5e_xdp_buff *
> array.
> Need to give it deeper thoughts...
>
> struct mlx5e_xdp_buff {
> struct xdp_buff *xdp;
> struct mlx5_cqe64 *cqe;
> struct mlx5e_rq *rq;
> };
This was actually my original proposal; we discussed this back on v2 of
this patch series. People generally felt that the 'cb' field approach
(originally suggested by Jakub) was better. See the discussion starting
from here:
https://lore.kernel.org/r/20221123111431.7b54668e@kernel.org
-Toke
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