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The taprio qdisc does not currently pass the mqprio queue configuration down to the offloading device driver. So the driver cannot act upon the TXQ counts/offsets per TC, or upon the prio->tc map. It was probably assumed that the driver only wants to offload num_tc (see TC_MQPRIO_HW_OFFLOAD_TCS), which it can get from netdev_get_num_tc(), but there's clearly more to the mqprio configuration than that. I've considered 2 mechanisms to remedy that. First is to pass a struct tc_mqprio_qopt_offload as part of the tc_taprio_qopt_offload. The second is to make taprio actually call TC_SETUP_QDISC_MQPRIO, *in addition to* TC_SETUP_QDISC_TAPRIO. The difference is that in the first case, existing drivers (offloading or not) all ignore taprio's mqprio portion currently, whereas in the second case, we could control whether to call TC_SETUP_QDISC_MQPRIO, based on a new capability. The question is which approach would be better. I'm afraid that calling TC_SETUP_QDISC_MQPRIO unconditionally (not based on a taprio capability bit) would risk introducing regressions. For example, taprio doesn't populate (or validate) qopt->hw, as well as mqprio.flags, mqprio.shaper, mqprio.min_rate, mqprio.max_rate. In comparison, adding a capability is functionally equivalent to just passing the mqprio in a way that drivers can ignore it, except it's slightly more complicated to use it (need to set the capability). Ultimately, what made me go for the "mqprio in taprio" variant was that it's easier for offloading drivers to interpret the mqprio qopt slightly differently when it comes from taprio vs when it comes from mqprio, should that ever become necessary. Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.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
be rendered in a number of formats, like HTML and PDF. Please read
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.