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Subject: Re: [RFC][PATCH 2/3] perf: Take a hot regs snapshot for trace
 events
From: Peter Zijlstra <peterz@infradead.org>
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Date: Wed, 03 Mar 2010 18:16:35 +0100
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On Wed, 2010-03-03 at 12:07 -0500, Steven Rostedt wrote:
> oops, my bad :-), I thought this was in the x86 arch directory. For the
> University, I was helping them with adding trace points for page faults
> when I came across this in arch/x86/mm/fault.c:
> 
>         perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS, 1, 0, regs, address);
> 
> 
> This is what I actually was wondering about. Why is it a "perf only"
> trace point instead of a TRACE_EVENT()?

Because I wanted to make perf usable without having to rely on funny
tracepoints. That is, I am less worried about committing software
counters to ABI than I am about TRACE_EVENT(), which still gives me a
terribly uncomfortable feeling.

Also, building with all CONFIG_TRACE_*=n will still yield a usable perf,
which is something the embedded people might fancy, all that TRACE stuff
adds lots of code.