netdev - Re: [PATCH bpf-next V2 1/5] igc: enable and fix RX hash usage by netstack

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Date:   Tue, 25 Apr 2023 10:43:02 +0200
From:   Jesper Dangaard Brouer <jbrouer@...hat.com>
To:     davem@...emloft.net, bpf@...r.kernel.org, daniel@...earbox.net
Cc:     brouer@...hat.com, netdev@...r.kernel.org, martin.lau@...nel.org,
        ast@...nel.org, alexandr.lobakin@...el.com,
        larysa.zaremba@...el.com, xdp-hints@...-project.net,
        John Fastabend <john.fastabend@...il.com>,
        Tony Nguyen <anthony.l.nguyen@...el.com>,
        yoong.siang.song@...el.com, intel-wired-lan@...ts.osuosl.org,
        pabeni@...hat.com, jesse.brandeburg@...el.com,
        Stanislav Fomichev <sdf@...gle.com>, kuba@...nel.org,
        edumazet@...gle.com, hawk@...nel.org,
        Toke Høiland-Jørgensen <toke@...hat.com>
Subject: Re: [PATCH bpf-next V2 1/5] igc: enable and fix RX hash usage by
 netstack


On 24/04/2023 21.17, John Fastabend wrote:
>>> Just curious why not copy the logic from the other driver fms10k, ice, ect.
>>>
>>> 	skb_set_hash(skb, le32_to_cpu(rx_desc->wb.lower.hi_dword.rss),
>>> 		     (IXGBE_RSS_L4_TYPES_MASK & (1ul << rss_type)) ?
>>> 		     PKT_HASH_TYPE_L4 : PKT_HASH_TYPE_L3);
>> Detail: This code mis-categorize (e.g. ARP) PKT_HASH_TYPE_L2 as
>> PKT_HASH_TYPE_L3, but as core reduces this further to one SKB bit, it
>> doesn't really matter.
>>
>>> avoiding the table logic. Do the driver folks care?
>> The define IXGBE_RSS_L4_TYPES_MASK becomes the "table" logic as a 1-bit
>> true/false table.  It is a more compact table, let me know if this is
>> preferred.
>>
>> Yes, it is really upto driver maintainer people to decide, what code is
>> preferred ?
 >
> Yeah doesn't matter much to me either way. I was just looking at code
> compared to ice driver while reviewing.

My preference is to apply this patchset. We/I can easily followup and
change this to use the more compact approach later (if someone prefers).

I know net-next is "closed", but this patchset was posted prior to the
close.  Plus, a number of companies are waiting for the XDP-hint for HW
RX timestamp.  The support for driver stmmac is already in net-next
(commit e3f9c3e34840 ("net: stmmac: add Rx HWTS metadata to XDP receive
pkt")). Thus, it would be a help if both igc+stmmac changes land in same
kernel version, as both drivers are being evaluated by these companies.

Pretty please,
--Jesper