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Message-ID: <448dd952-be53-6930-c7fb-fc3474ce17f7@engleder-embedded.com>
Date: Thu, 26 Jan 2023 20:21:15 +0100
From: Gerhard Engleder <gerhard@...leder-embedded.com>
To: Vladimir Oltean <vladimir.oltean@....com>, netdev@...r.kernel.org
Cc: "David S. Miller" <davem@...emloft.net>,
Eric Dumazet <edumazet@...gle.com>,
Jakub Kicinski <kuba@...nel.org>,
Paolo Abeni <pabeni@...hat.com>,
Claudiu Manoil <claudiu.manoil@....com>,
Vinicius Costa Gomes <vinicius.gomes@...el.com>,
Kurt Kanzenbach <kurt@...utronix.de>,
Jacob Keller <jacob.e.keller@...el.com>,
Horatiu Vultur <horatiu.vultur@...rochip.com>,
Siddharth Vadapalli <s-vadapalli@...com>,
Roger Quadros <rogerq@...nel.org>
Subject: Re: [PATCH v2 net-next 15/15] net/sched: taprio: only calculate gate
mask per TXQ for igc, stmmac and tsnep
On 26.01.23 13:53, Vladimir Oltean wrote:
> There are 2 classes of in-tree drivers currently:
>
> - those who act upon struct tc_taprio_sched_entry :: gate_mask as if it
> holds a bit mask of TXQs
>
> - those who act upon the gate_mask as if it holds a bit mask of TCs
>
> When it comes to the standard, IEEE 802.1Q-2018 does say this in the
> second paragraph of section 8.6.8.4 Enhancements for scheduled traffic:
>
> | A gate control list associated with each Port contains an ordered list
> | of gate operations. Each gate operation changes the transmission gate
> | state for the gate associated with each of the Port's traffic class
> | queues and allows associated control operations to be scheduled.
>
> In typically obtuse language, it refers to a "traffic class queue"
> rather than a "traffic class" or a "queue". But careful reading of
> 802.1Q clarifies that "traffic class" and "queue" are in fact
> synonymous (see 8.6.6 Queuing frames):
>
> | A queue in this context is not necessarily a single FIFO data structure.
> | A queue is a record of all frames of a given traffic class awaiting
> | transmission on a given Bridge Port. The structure of this record is not
> | specified.
>
> i.o.w. their definition of "queue" isn't the Linux TX queue.
>
> The gate_mask really is input into taprio via its UAPI as a mask of
> traffic classes, but taprio_sched_to_offload() converts it into a TXQ
> mask.
>
> The breakdown of drivers which handle TC_SETUP_QDISC_TAPRIO is:
>
> - hellcreek, felix, sja1105: these are DSA switches, it's not even very
> clear what TXQs correspond to, other than purely software constructs.
> For felix and sja1105, I can confirm that only the mqprio
> configuration with 8 TCs and 1 TXQ per TC makes sense. So it's fine to
> convert these to a gate mask per TC.
>
> - enetc: I have the hardware and can confirm that the gate mask is per
> TC, and affects all TXQs (BD rings) configured for that priority.
>
> - igc: in igc_save_qbv_schedule(), the gate_mask is clearly interpreted
> to be per-TXQ.
>
> - tsnep: Gerhard Engleder clarifies that even though this hardware
> supports at most 1 TXQ per TC, the TXQ indices may be different from
> the TC values themselves, and it is the TXQ indices that matter to
> this hardware. So keep it per-TXQ as well.
>
> - stmmac: I have a GMAC datasheet, and in the EST section it does
> specify that the gate events are per TXQ rather than per TC.
>
> - lan966x: again, this is a switch, and while not a DSA one, the way in
> which it implements lan966x_mqprio_add() - by only allowing num_tc ==
> NUM_PRIO_QUEUES (8) - makes it clear to me that TXQs are a purely
> software construct here as well. They seem to map 1:1 with TCs.
>
> - am65_cpsw: from looking at am65_cpsw_est_set_sched_cmds(), I get the
> impression that the fetch_allow variable is treated like a prio_mask.
> I haven't studied this driver's interpretation of the prio_tc_map, but
> that definitely sounds closer to a per-TC gate mask rather than a
> per-TXQ one.
>
> Based on this breakdown, we have 6 drivers with a gate mask per TC and
> 3 with a gate mask per TXQ. So let's make the gate mask per TXQ the
> opt-in and the gate mask per TC the default.
>
> Benefit from the TC_QUERY_CAPS feature that Jakub suggested we add, and
> query the device driver before calling the proper ndo_setup_tc(), and
> figure out if it expects one or the other format.
>
> Cc: Gerhard Engleder <gerhard@...leder-embedded.com>
> Cc: Horatiu Vultur <horatiu.vultur@...rochip.com>
> Cc: Siddharth Vadapalli <s-vadapalli@...com>
> Cc: Roger Quadros <rogerq@...nel.org>
> Signed-off-by: Vladimir Oltean <vladimir.oltean@....com>
> ---
> v1->v2:
> - rewrite commit message
> - also opt in stmmac and tsnep
>
> drivers/net/ethernet/engleder/tsnep_tc.c | 21 +++++++++++++++++
> drivers/net/ethernet/intel/igc/igc_main.c | 23 +++++++++++++++++++
> drivers/net/ethernet/stmicro/stmmac/hwif.h | 5 ++++
> .../net/ethernet/stmicro/stmmac/stmmac_main.c | 2 ++
> .../net/ethernet/stmicro/stmmac/stmmac_tc.c | 20 ++++++++++++++++
> include/net/pkt_sched.h | 1 +
> net/sched/sch_taprio.c | 11 ++++++---
> 7 files changed, 80 insertions(+), 3 deletions(-)
Reviewed-by: Gerhard Engleder <gerhard@...leder-embedded.com>
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