Subject: [RFC PATCH 0/3] Faster than SLAB caching of SKBs with qmempool (backed by alf_queue)

From: Jesper Dangaard Brouer <[email-masked]>
Date: Wed, 10 Dec 2014 15:15:07 +0100

The network stack have some use-cases that puts some extreme demands
on the memory allocator.  One use-case, 10Gbit/s wirespeed at smallest
packet size[1], requires handling a packet every 67.2 ns (nanosec).

Micro benchmarking[2] the SLUB allocator (with skb size 256bytes
elements), show "fast-path" instant reuse only costs 19 ns, but a
closer to network usage pattern show the cost rise to 45 ns.

This patchset introduce a quick mempool (qmempool), which when used
in-front of the SKB (sk_buff) kmem_cache, saves 12 ns on "fast-path"
drop in iptables "raw" table, but more importantly saves 40 ns with
IP-forwarding, which were hitting the slower SLUB use-case.

One of the building blocks for achieving this speedup is a cmpxchg
based Lock-Free queue that supports bulking, named alf_queue for
Array-based Lock-Free queue.  By bulking elements (pointers) from the
queue, the cost of the cmpxchg (approx 8 ns) is amortized over several
elements.

 Patch1: alf_queue (Lock-Free queue)

 Patch2: qmempool using alf_queue

 Patch3: usage of qmempool for SKB caching

Notice, this patchset depend on introduction of napi_alloc_skb(),
which is part of Alexander Duyck's work patchset [3].

Different correctness tests and micro benchmarks are avail via my
github repo "prototype-kernel"[4], where the alf_queue and qmempool is
also kept in sync with this patchset.

Links:
 [1]: http://netoptimizer.blogspot.dk/2014/05/the-calculations-10gbits-wirespeed.html
 [2]: https://github.com/netoptimizer/prototype-kernel/blob/master/kernel/mm/qmempool_bench.c
 [3]: http://thread.gmane.org/gmane.linux.network/342347
 [4]: https://github.com/netoptimizer/prototype-kernel

---

Jesper Dangaard Brouer (3):
      net: use qmempool in-front of sk_buff kmem_cache
      mm: qmempool - quick queue based memory pool
      lib: adding an Array-based Lock-Free (ALF) queue

 include/linux/alf_queue.h |  303 ++++++++++++++++++++++++++++++++++++++++++
 include/linux/qmempool.h  |  205 +++++++++++++++++++++++++++++
 include/linux/skbuff.h    |    4 -
 lib/Kconfig               |   13 ++
 lib/Makefile              |    2 
 lib/alf_queue.c           |   47 +++++++
 mm/Kconfig                |   12 ++
 mm/Makefile               |    1 
 mm/qmempool.c             |  322 +++++++++++++++++++++++++++++++++++++++++++++
 net/core/dev.c            |    5 +
 net/core/skbuff.c         |   43 +++++-
 11 files changed, 950 insertions(+), 7 deletions(-)
 create mode 100644 include/linux/alf_queue.h
 create mode 100644 include/linux/qmempool.h
 create mode 100644 lib/alf_queue.c
 create mode 100644 mm/qmempool.c

-- 
Best regards,
  Jesper Dangaard Brouer
  MSc.CS, Sr. Network Kernel Developer at Red Hat
  Author of http://www.iptv-analyzer.org
  LinkedIn: http://www.linkedin.com/in/brouer

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