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

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Date:	Fri, 12 Jun 2009 10:17:50 -0700
From:	Randy Dunlap <randy.dunlap@...cle.com>
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

Mike Frysinger wrote:
> Help out arch porters who want to support perf counters by listing some
> basic requirements.
> 
> Signed-off-by: Mike Frysinger <vapier@...too.org>
> ---
> i imagine more details would be good, but this is a starting point and
> better than nothing
> 
>  init/Kconfig          |    2 ++
>  tools/perf/design.txt |   15 +++++++++++++++
>  2 files changed, 17 insertions(+), 0 deletions(-)
> 
> diff --git a/init/Kconfig b/init/Kconfig
> index c649657..20f85b1 100644
> --- a/init/Kconfig
> +++ b/init/Kconfig
> @@ -936,6 +936,8 @@ config AIO
>  
>  config HAVE_PERF_COUNTERS
>  	bool
> +	help
> +	  See end of tools/perf/design.txt

How about
	  See "Arch requirements" in tools/perf/design.txt
since it doesn't need to be at the end of the file forever.

>  
>  menu "Performance Counters"
>  
> 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.


-- 
~Randy
LPC 2009, Sept. 23-25, Portland, Oregon
http://linuxplumbersconf.org/2009/
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