[PATCH v5 00/10] latched RB-trees and __module_address()

From: Peter Zijlstra
Date: Mon Apr 13 2015 - 10:18:44 EST

This series is aimed at making __module_address() go fast(er).

The reason for doing so is that most stack unwinders use kernel_text_address()
to validate each frame. Perf and ftrace (can) end up doing a lot of stack
traces from performance sensitive code.

On the way there it:
- annotates and sanitizes module locking
- introduces the latched RB-tree
- employs it to make __module_address() go fast.

I've build and boot tested this on x86_64 with modules and lockdep
enabled. Performance numbers (below) are done with lockdep disabled.

As previously mentioned; the reason for writing the latched RB-tree as generic
code is mostly for clarity/documentation purposes; as there are a number of
separate and non trivial bits to the complete solution.

As measued on my ivb-ep system with 84 modules loaded; prior to patching
the test module (below) reports (cache hot, performance cpufreq):

avg +- stdev
Before: 611 +- 10 [ns] per __module_address() call
After: 17 +- 5 [ns] per __module_address() call

PMI measurements for a cpu running loops in a module (also [ns]):

Before: Mean: 2719 +- 1, Stdev: 214, Samples: 40036
After: Mean: 947 +- 0, Stdev: 132, Samples: 40037

Note; I have also tested things like: perf record -a -g modprobe
mod_test, to make 'sure' to hit some of the more interesting paths.

Changes since last time:

- reworked generic latch_tree API (Lai Jiangshan)
- reworked module bounds (me)
- reworked all the testing code (not included)

Rusty, please consider merging this (for 4.2, I know its the merge window, no

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