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:
avg +- stdev
Before: 1689 +- 287 [ns] per __module_address() call
After: 137 +- 38 [ns] per __module_address() call
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:
- depend on CONFIG_PERF_EVENTS || CONFIG_TRACING -- akpm
- use within_module() for jump_labels -- rusty
- minor comment changes -- Compudj, mingo
Rusty, please consider merging this.
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