linux-kernel - Re: [PATCH 0/8] latched RB-trees and __module

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Message-ID: <20150318143804.GN23123@twins.programming.kicks-ass.net>
Date:	Wed, 18 Mar 2015 15:38:04 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Christoph Hellwig <hch@...radead.org>
Cc:	mingo@...nel.org, rusty@...tcorp.com.au,
	mathieu.desnoyers@...icios.com, oleg@...hat.com,
	paulmck@...ux.vnet.ibm.com, torvalds@...ux-foundation.org,
	linux-kernel@...r.kernel.org, andi@...stfloor.org,
	rostedt@...dmis.org, tglx@...utronix.de
Subject: Re: [PATCH 0/8] latched RB-trees and __module_address()

On Wed, Mar 18, 2015 at 07:21:14AM -0700, Christoph Hellwig wrote:
> On Wed, Mar 18, 2015 at 02:36:26PM +0100, Peter Zijlstra wrote:
> > This series is aimed at making __module_address() go fast(er).
> 
> What users do hit this so hard that it matters?  Seems like the jump
> label code uses it directly and throgh __module_text_address, and krobes
> use it throug __module_text_address.  Is it the pageattr code or
> lockdep?

>From 7/8:

"One of the users of this is kernel_text_address() which is employed
in many stack unwinders; which in turn are used by perf-callchain and
ftrace (possibly from NMI context).

So by optimizing __module_address() we optimize many stack unwinders
which are used by both perf and tracing in performance sensitive code."

> Also seems interesting that both __module_address and __module_text_address
> are exported, but don't seem to have modular users.

Yeah and a few others too iirc.
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