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

From: Ingo Molnar
Date: Mon Apr 13 2015 - 13:02:51 EST

* Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:

> 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

Those are some pretty impressive speedups!

I suspect the 900 nsecs residual PMI overhead is due to other, overly
bloated PMI (perf) processing costs?

> 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 rush)

So modulo the mostly trivial feedback I gave, it looks all good to me
as well, feel free to also add my:

Reviewed-by: Ingo Molnar <mingo@xxxxxxxxxx>


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