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d365c9bca3
15 years after Tom Herbert added skb->ooo_okay, only TCP transport
benefits from it.
We can support other transports directly from skb_set_owner_w().
If no other TX packet for this socket is in a host queue (qdisc, NIC queue)
there is no risk of self-inflicted reordering, we can set skb->ooo_okay.
This allows netdev_pick_tx() to choose a TX queue based on XPS settings,
instead of reusing the queue chosen at the time the first packet was sent
for connected sockets.
Tested:
500 concurrent UDP_RR connected UDP flows, host with 32 TX queues,
512 cpus, XPS setup.
super_netperf 500 -t UDP_RR -H <host> -l 1000 -- -r 100,100 -Nn &
This patch saves between 10% and 20% of cycles, depending on how
process scheduler migrates threads among cpus.
Using following bpftrace script, we can see the effect on Qdisc/NIC tx queues
being better used (less cache line misses).
bpftrace -e '
k:__dev_queue_xmit { @start[cpu] = nsecs; }
kr:__dev_queue_xmit {
if (@start[cpu]) {
$delay = nsecs - @start[cpu];
delete(@start[cpu]);
@__dev_queue_xmit_ns = hist($delay);
}
}
END { clear(@start); }'
Before:
@__dev_queue_xmit_ns:
[128, 256) 6 | |
[256, 512) 116283 | |
[512, 1K) 1888205 |@@@@@@@@@@@ |
[1K, 2K)
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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 reStructuredText 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.