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Date: Thu, 19 Mar 2015 23:04:33 +0100
From: Peter Zijlstra <peterz@infradead.org>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: mingo@kernel.org, rusty@rustcorp.com.au, mathieu.desnoyers@efficios.com,
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        David Woodhouse <David.Woodhouse@intel.com>,
        Rik van Riel <riel@redhat.com>
Subject: Re: [PATCH 6/8] rbtree: Implement generic latch_tree
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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.