netdev - Re: [PATCH bpf RFC-V3 1/5] xdp: rss hash types representation

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Date:   Thu, 30 Mar 2023 21:08:27 +0200
From:   Jesper Dangaard Brouer <jbrouer@...hat.com>
To:     Stanislav Fomichev <sdf@...gle.com>,
        Jesper Dangaard Brouer <jbrouer@...hat.com>
Cc:     brouer@...hat.com, bpf@...r.kernel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, martin.lau@...nel.org,
        ast@...nel.org, daniel@...earbox.net, alexandr.lobakin@...el.com,
        larysa.zaremba@...el.com, xdp-hints@...-project.net,
        anthony.l.nguyen@...el.com, yoong.siang.song@...el.com,
        boon.leong.ong@...el.com, intel-wired-lan@...ts.osuosl.org,
        pabeni@...hat.com, jesse.brandeburg@...el.com, kuba@...nel.org,
        edumazet@...gle.com, john.fastabend@...il.com, hawk@...nel.org,
        davem@...emloft.net
Subject: Re: [PATCH bpf RFC-V3 1/5] xdp: rss hash types representation


On 30/03/2023 21.02, Stanislav Fomichev wrote:
> On Thu, Mar 30, 2023 at 11:56 AM Jesper Dangaard Brouer
>>
>> On 30/03/2023 20.35, Stanislav Fomichev wrote:
>>> On 03/30, Jesper Dangaard Brouer wrote:
[...]
>> [...]
>>>> diff --git a/net/core/xdp.c b/net/core/xdp.c
>>>> index 528d4b37983d..38d2dee16b47 100644
>>>> --- a/net/core/xdp.c
>>>> +++ b/net/core/xdp.c
>>>> @@ -734,14 +734,22 @@ __bpf_kfunc int
>>>> bpf_xdp_metadata_rx_timestamp(const struct xdp_md *ctx, u64 *tim
>>>>     * bpf_xdp_metadata_rx_hash - Read XDP frame RX hash.
>>>>     * @ctx: XDP context pointer.
>>>>     * @hash: Return value pointer.
>>>> + * @rss_type: Return value pointer for RSS type.
>>>> + *
>>>> + * The RSS hash type (@rss_type) specifies what portion of packet headers NIC
>>>> + * hardware were used when calculating RSS hash value.  The type combinations
>>>> + * are defined via &enum xdp_rss_hash_type and individual bits can be decoded
>>>> + * via &enum xdp_rss_type_bits.
>>>>     *
>>>>     * Return:
>>>>     * * Returns 0 on success or ``-errno`` on error.
>>>>     * * ``-EOPNOTSUPP`` : means device driver doesn't implement kfunc
>>>>     * * ``-ENODATA``    : means no RX-hash available for this frame
>>>>     */
>>>> -__bpf_kfunc int bpf_xdp_metadata_rx_hash(const struct xdp_md *ctx,
>>>> u32 *hash)
>>>> +__bpf_kfunc int bpf_xdp_metadata_rx_hash(const struct xdp_md *ctx,
>>>> u32 *hash,
>>>> +                     enum xdp_rss_hash_type *rss_type)
>>>>    {
>>> [..]
>>>
>>>> +    BTF_TYPE_EMIT(enum xdp_rss_type_bits);
>>> nit: Do we still need this with an extra argument?
>>>
>> Yes, unfortunately (compiler optimizes out enum xdp_rss_type_bits).
>> Do notice the difference xdp_rss_type_bits vs xdp_rss_hash_type.
>> We don't need it for "xdp_rss_hash_type" but need it for
>> "xdp_rss_type_bits".
 >
> Ah, I missed that. Then why not expose xdp_rss_type_bits?
> Keep xdp_rss_hash_type for internal drivers' tables, and export the
> enum with the bits?

Great suggestion, xdp_rss_hash_type will be internal for drivers.
I will do that in V4.

--Jesper