Re: [PATCH v5 00/10] latched RB-trees and __module_address()
From: Rusty Russell
Date: Mon Apr 13 2015 - 22:58:07 EST
Peter Zijlstra <peterz@xxxxxxxxxxxxx> writes:
> 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
I was tempted to sneak in those module rcu fixes for 4.1, but seeing
Ingo's comments I'll wait for 4.2.
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