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

From: Jesper Dangaard Brouer
Date: Wed Dec 10 2014 - 09:15:56 EST

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

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.

[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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