linux-kernel - Re: [PATCH 6/8] rbtree: Implement generic latch

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Message-ID: <20150319220433.GS2896@worktop.programming.kicks-ass.net>
Date:	Thu, 19 Mar 2015 23:04:33 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Andrew Morton <akpm@...ux-foundation.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,
	Michel Lespinasse <walken@...gle.com>,
	Andrea Arcangeli <aarcange@...hat.com>,
	David Woodhouse <David.Woodhouse@...el.com>,
	Rik van Riel <riel@...hat.com>
Subject: Re: [PATCH 6/8] rbtree: Implement generic latch_tree

On Thu, Mar 19, 2015 at 01:58:33PM -0700, Andrew Morton wrote:
> OK.  This code is basically required to support perf/ftrace and
> modules, yes?  Presumably small and space-constrained systems aren't
> using either, so they don't take the hit.
> 
> However CONFIG_MODULES systems which aren't using perf/ftrace _do_ take
> a hit.  How many systems are we talking here?  All non-x86?

No, there's plenty !x86 systems that have NMI and perf/ftrace, in fact,
ARM has them (FIQ) and there's event some ARM chips that use them for
perf (i.MX6 is one).

But sure, we could make this depend on CONFIG_PERF_EVENTS ||
CONFIG_TRACING.
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