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Mainline Linux tree for various devices, only for fun :)
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John Fastabend says: ==================== lockless qdisc series This series adds support for building lockless qdiscs. This is the result of noticing the qdisc lock is a common hot-spot in perf analysis of the Linux network stack, especially when testing with high packet per second rates. However, nothing is free and most qdiscs rely on the qdisc lock for their data structures so each qdisc must be converted on a case by case basis. In this series, to kick things off, we make pfifo_fast, mq, and mqprio lockless. Follow up series can address additional qdiscs as needed. For example sch_tbf might be useful. To allow this the lockless design is an opt-in flag. In some future utopia we convert all qdiscs and we get to drop this case analysis, but in order to make progress we live in the real-world. There are also a handful of optimizations I have behind this series and a few code cleanups that I couldn't figure out how to fit neatly into this series with out increasing the patch count. Once this is in additional patches can address this. The most notable is in skb_dequeue we can push the consumer lock out a bit and consume multiple skbs off the skb_array in pfifo fast per iteration. Ideally we could push arrays of packets at drivers as well but we would need the infrastructure for this. The other notable improvement is to do less locking in the overrun cases where bad tx queue list and gso_skb are being hit. Although, nice in theory in practice this is the error case and I haven't found a benchmark where this matters yet. For testing... My first test case uses multiple containers (via cilium) where multiple client containers use 'wrk' to benchmark connections with a server container running lighttpd. Where lighttpd is configured to use multiple threads, one per core. Additionally this test has a proxy agent running so all traffic takes an extra hop through a proxy container. In these cases each TCP packet traverses the egress qdisc layer at least four times and the ingress qdisc layer an additional four times. This makes for a good stress test IMO, perf details below. The other micro-benchmark I run is injecting packets directly into qdisc layer using pktgen. This uses the benchmark script, ./pktgen_bench_xmit_mode_queue_xmit.sh Benchmarks taken in two cases, "base" running latest net-next no changes to qdisc layer and "qdisc" tests run with qdisc lockless updates. Numbers reported in req/sec. All virtual 'veth' devices run with pfifo_fast in the qdisc test case. `wrk -t16 -c $conns -d30 "http://[$SERVER_IP4]:80"` conns 16 32 64 1024 ----------------------------------------------- base: 18831 20201 21393 29151 qdisc: 19309 21063 23899 29265 notice in all cases we see performance improvement when running with qdisc case. Microbenchmarks using pktgen are as follows, `pktgen_bench_xmit_mode_queue_xmit.sh -t 1 -i eth2 -c 20000000 base(mq): 2.1Mpps base(pfifo_fast): 2.1Mpps qdisc(mq): 2.6Mpps qdisc(pfifo_fast): 2.6Mpps notice numbers are the same for mq and pfifo_fast because only testing a single thread here. In both tests we see a nice bump in performance gain. The key with 'mq' is it is already per txq ring so contention is minimal in the above cases. Qdiscs such as tbf or htb which have more contention will likely show larger gains when/if lockless versions are implemented. Thanks to everyone who helped with this work especially Daniel Borkmann, Eric Dumazet and Willem de Bruijn for discussing the design and reviewing versions of the code. Changes from the RFC: dropped a couple patches off the end, fixed a bug with skb_queue_walk_safe not unlinking skb in all cases, fixed a lockdep splat with pfifo_fast_destroy not calling *_bh lock variant, addressed _most_ of Willem's comments, there was a bug in the bulk locking (final patch) of the RFC series. @Willem, I left out lockdep annotation for a follow on series to add lockdep more completely, rather than just in code I touched. Comments and feedback welcome. ==================== Signed-off-by: David S. Miller <davem@davemloft.net> |
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Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. 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.