linux-kernel - Re: [PATCH] perf_counters: start documenting HAVE_PERF

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Message-ID: <20090614094111.GE832@linux-sh.org>
Date:	Sun, 14 Jun 2009 18:41:11 +0900
From:	Paul Mundt <lethal@...ux-sh.org>
To:	Mike Frysinger <vapier@...too.org>
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Paul Mackerras <paulus@...ba.org>, Ingo Molnar <mingo@...e.hu>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] perf_counters: start documenting HAVE_PERF_COUNTERS requirements

On Fri, Jun 12, 2009 at 01:27:12PM -0400, Mike Frysinger wrote:
> diff --git a/tools/perf/design.txt b/tools/perf/design.txt
> index 860e116..f71e0d2 100644
> --- a/tools/perf/design.txt
> +++ b/tools/perf/design.txt
> @@ -440,3 +440,18 @@ by this process or by another, and doesn't affect any counters that
>  this process has created on other processes.  It only enables or
>  disables the group leaders, not any other members in the groups.
>  
> +
> +Arch requirements
> +-----------------
> +
> +If your architecture does not have hardware performance metrics, you can
> +still use the generic software counters based on hrtimers for sampling.
> +
> +So to start with, in order to add HAVE_PERF_COUNTERS to your Kconfig, you
> +will need at least this:
> +	- asm/perf_counter.h - a basic stub will suffice at first
> +	- support for atomic64 types (and associated helper functions)
> +	- set_perf_counter_pending() implemented
> +
> +If your architecture does have hardware capabilities, you can override the
> +weak stub hw_perf_counter_init() to register hardware counters.

It would be nice to see this in arch/Kconfig instead, as that tends to
provide a centralized checklist for new features, especially when they
are non-trivial. At least I found the arch/Kconfig bits very helpful for
things like tracehook support, without having to grovel around
Documentation for verbose design documents that I otherwise couldn't care
less about.
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