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ba27b4cdaa
With commitc5ad119fb6("net: sched: pfifo_fast use skb_array") pfifo_fast no longer benefit from the TCQ_F_CAN_BYPASS optimization. Due to retpolines the cost of the enqueue()/dequeue() pair has become relevant and we observe measurable regression for the uncontended scenario when the packet-rate is below line rate. After commit46b1c18f9d("net: sched: put back q.qlen into a single location") we can check for empty qdisc with a reasonably fast operation even for nolock qdiscs. This change extends TCQ_F_CAN_BYPASS support to nolock qdisc. The new chunk of code mirrors closely the existing one for traditional qdisc, leveraging a newly introduced helper to read atomically the qdisc length. Tested with pktgen in queue xmit mode, with pfifo_fast, a MQ device, and MQ root qdisc: threads vanilla patched kpps kpps 1 2465 2889 2 4304 5188 4 7898 9589 Same as above, but with a single queue device: threads vanilla patched kpps kpps 1 2556 2827 2 2900 2900 4 5000 5000 8 4700 4700 No mesaurable changes in the contended scenarios, and more 10% improvement in the uncontended ones. v1 -> v2: - rebased after flag name change Signed-off-by: Paolo Abeni <pabeni@redhat.com> Tested-by: Ivan Vecera <ivecera@redhat.com> Reviewed-by: Eric Dumazet <edumazet@google.com> Reviewed-by: Ivan Vecera <ivecera@redhat.com> Signed-off-by: David S. Miller <davem@davemloft.net>
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.