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By imposing that the last TXQ of TC i is smaller than the first TXQ of any TC j (j := i+1 .. n), mqprio imposes a strict ordering condition for the TXQ indices (they must increase as TCs increase). Claudiu points out that the complexity of the TXQ count validation is too high for this logic, i.e. instead of iterating over j, it is sufficient that the TXQ indices of TC i and i + 1 are ordered, and that will eventually ensure global ordering. This is true, however it doesn't appear to me that is what the code really intended to do. Instead, based on the comments, it just wanted to check for overlaps (and this isn't how one does that). So the following mqprio configuration, which I had recommended to Vinicius more than once for igb/igc (to account for the fact that on this hardware, lower numbered TXQs have higher dequeue priority than higher ones): num_tc 4 map 0 1 2 3 queues 1@3 1@2 1@1 1@0 is in fact denied today by mqprio. The full story is that in fact, it's only denied with "hw 0"; if hardware offloading is requested, mqprio defers TXQ range overlap validation to the device driver (a strange decision in itself). This is most certainly a bug, but it's not one that has any merit for being fixed on "stable" as far as I can tell. This is because mqprio always rejected a configuration which was in fact valid, and this has shaped the way in which mqprio configuration scripts got built for various hardware (see igb/igc in the link below). Therefore, one could consider it to be merely an improvement for mqprio to allow reverse TC:TXQ mappings. Link: https://patchwork.kernel.org/project/netdevbpf/patch/20230130173145.475943-9-vladimir.oltean@nxp.com/#25188310 Link: https://patchwork.kernel.org/project/netdevbpf/patch/20230128010719.2182346-6-vladimir.oltean@nxp.com/#25186442 Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com> Reviewed-by: Simon Horman <simon.horman@corigine.com> Reviewed-by: Gerhard Engleder <gerhard@engleder-embedded.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.