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Message-ID: <04256caf-aa28-7e0a-59b1-ecf2b237c96f@redhat.com>
Date: Thu, 30 Mar 2023 20:56:19 +0200
From: Jesper Dangaard Brouer <jbrouer@...hat.com>
To: Stanislav Fomichev <sdf@...gle.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 20.35, Stanislav Fomichev wrote:
> On 03/30, Jesper Dangaard Brouer wrote:
>> The RSS hash type specifies what portion of packet data NIC hardware used
>> when calculating RSS hash value. The RSS types are focused on Internet
>> traffic protocols at OSI layers L3 and L4. L2 (e.g. ARP) often get hash
>> value zero and no RSS type. For L3 focused on IPv4 vs. IPv6, and L4
>> primarily TCP vs UDP, but some hardware supports SCTP.
>
>> Hardware RSS types are differently encoded for each hardware NIC. Most
>> hardware represent RSS hash type as a number. Determining L3 vs L4 often
>> requires a mapping table as there often isn't a pattern or sorting
>> according to ISO layer.
>
>> The patch introduce a XDP RSS hash type (enum xdp_rss_hash_type) that
>> contain combinations to be used by drivers, which gets build up with bits
>> from enum xdp_rss_type_bits. Both enum xdp_rss_type_bits and
>> xdp_rss_hash_type get exposed to BPF via BTF, and it is up to the
>> BPF-programmer to match using these defines.
>
>> This proposal change the kfunc API bpf_xdp_metadata_rx_hash() adding
>> a pointer value argument for provide the RSS hash type.
>
>> Signed-off-by: Jesper Dangaard Brouer <brouer@...hat.com>
>> ---
>> include/linux/netdevice.h | 3 ++-
>> include/net/xdp.h | 46 +++++++++++++++++++++++++++++++++++++++++++++
>> net/core/xdp.c | 10 +++++++++-
>> 3 files changed, 57 insertions(+), 2 deletions(-)
>
[...]
>> 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".
--Jesper
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