From: Rusty Russell <rusty@rustcorp.com.au>
To: Peter Zijlstra <peterz@infradead.org>, mingo@kernel.org,
        mathieu.desnoyers@efficios.com, oleg@redhat.com,
        paulmck@linux.vnet.ibm.com, torvalds@linux-foundation.org
Cc: linux-kernel@vger.kernel.org, andi@firstfloor.org, rostedt@goodmis.org,
        tglx@linutronix.de, laijs@cn.fujitsu.com, linux@horizon.com,
        peterz@infradead.org
Subject: Re: [PATCH v5 00/10] latched RB-trees and __module_address()
In-Reply-To: <20150413141126.756350256@infradead.org>
References: <20150413141126.756350256@infradead.org>
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Date: Tue, 14 Apr 2015 12:27:05 +0930
Message-ID: <87wq1fs9ha.fsf@rustcorp.com.au>
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Peter Zijlstra <peterz@infradead.org> 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
> rush)

I was tempted to sneak in those module rcu fixes for 4.1, but seeing
Ingo's comments I'll wait for 4.2.

Thanks,
Rusty.
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