linux-kernel - Re: [PATCH v6 0/9] latched RB-trees and __module

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Date:	Thu, 07 May 2015 10:50:39 +0930
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	Peter Zijlstra <peterz@...radead.org>, mingo@...nel.org,
	mathieu.desnoyers@...icios.com, oleg@...hat.com,
	paulmck@...ux.vnet.ibm.com, torvalds@...ux-foundation.org
Cc:	linux-kernel@...r.kernel.org, andi@...stfloor.org,
	rostedt@...dmis.org, tglx@...utronix.de, laijs@...fujitsu.com,
	linux@...izon.com, peterz@...radead.org
Subject: Re: [PATCH v6 0/9] latched RB-trees and __module_address()

Peter Zijlstra <peterz@...radead.org> writes:
> This series is aimed at making __module_address() go fast(er).

Acked-by: Rusty Russell <rusty@...tcorp.com.au> (module parts)

Since all the interesting stuff is not module-specific, assume
this is via Ingo?  Otherwise, I'll take it...

Thanks,
Rusty.

>
> 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 measured on my ivb-ep system with 84 modules loaded; the test module 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:
>
>  - rebased against Rusty's tree
>  - raw_read_seqcount_latch() -- (mingo)
>
> Based on rusty/linux.git/pending-rebases; please consider for 4.2
>
> Thanks!
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