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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. 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. This definitely sounds closer to a per-TC gate mask rather than a per-TXQ one, and TI documentation does seem to recomment an identity mapping between TCs and TXQs. However, Roger Quadros would like to do some testing before making changes, so I'm leaving this driver to operate as it did before, for now. Link with more details at the end. Based on this breakdown, we have 5 drivers with a gate mask per TC and 4 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. Link: https://patchwork.kernel.org/project/netdevbpf/patch/20230202003621.2679603-15-vladimir.oltean@nxp.com/#25193204 Cc: Horatiu Vultur <horatiu.vultur@microchip.com> Cc: Siddharth Vadapalli <s-vadapalli@ti.com> Cc: Roger Quadros <rogerq@kernel.org> Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com> Acked-by: Kurt Kanzenbach <kurt@linutronix.de> # hellcreek Reviewed-by: Gerhard Engleder <gerhard@engleder-embedded.com> Reviewed-by: Simon Horman <simon.horman@corigine.com> Signed-off-by: David S. Miller <davem@davemloft.net> |
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Linux kernel
============
There are several guides for kernel developers and users. These guides can
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Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.