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076433bd78
TCQ_F_CAN_BYPASS can be used by few qdiscs. Idea is that if we queue a packet to an empty qdisc, following dequeue() would pick it immediately. FQ can not use the generic TCQ_F_CAN_BYPASS code, because some additional checks need to be performed. This patch adds a similar fast path to FQ. Most of the time, qdisc is not throttled, and many packets can avoid bringing/touching at least four cache lines, and consuming 128bytes of memory to store the state of a flow. After this patch, netperf can send UDP packets about 13 % faster, and pktgen goes 30 % faster (when FQ is in the way), on a fast NIC. TCP traffic is also improved, thanks to a reduction of cache line misses. I have measured a 5 % increase of throughput on a tcp_rr intensive workload. tc -s -d qd sh dev eth1 ... qdisc fq 8004: parent 1:2 limit 10000p flow_limit 100p buckets 1024 orphan_mask 1023 quantum 3028b initial_quantum 15140b low_rate_threshold 550Kbit refill_delay 40ms timer_slack 10us horizon 10s horizon_drop Sent 5646784384 bytes 1985161 pkt (dropped 0, overlimits 0 requeues 0) backlog 0b 0p requeues 0 flows 122 (inactive 122 throttled 0) gc 0 highprio 0 fastpath 659990 throttled 27762 latency 8.57us Signed-off-by: Eric Dumazet <edumazet@google.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.