linux-kernel - Re: [PATCH 4/6] hw_breakpoints: Breakpoints arch ability don't need perf events

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Message-ID: <20110704133223.GB2963@in.ibm.com>
Date:	Mon, 4 Jul 2011 19:02:23 +0530
From:	"K.Prasad" <prasad@...ux.vnet.ibm.com>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	LKML <linux-kernel@...r.kernel.org>, linuxppc-dev@...ts.ozlabs.org,
	Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Will Deacon <will.deacon@....com>,
	Paul Mundt <lethal@...ux-sh.org>
Subject: Re: [PATCH 4/6] hw_breakpoints: Breakpoints arch ability don't need
 perf events

On Tue, May 24, 2011 at 11:52:25PM +0200, Frederic Weisbecker wrote:
> The breakpoint support ability in an arch is not related
> to the fact perf events is built or not. HAVE_HW_BREAKPOINT
> only shows an ability so this dependency makes no sense
> anymore. Archs that select HAVE_HW_BREAKPOINT already
> ensure that perf event is built.
> 
> Remove that dependency.
> 
> Signed-off-by: Frederic Weisbecker <fweisbec@...il.com>
> Cc: Ingo Molnar <mingo@...e.hu>
> Cc: Peter Zijlstra <a.p.zijlstra@...llo.nl>
> Cc: Will Deacon <will.deacon@....com>
> Cc: Prasad <prasad@...ux.vnet.ibm.com>
> Cc: Paul Mundt <lethal@...ux-sh.org>
> ---
>  arch/Kconfig |    1 -
>  1 files changed, 0 insertions(+), 1 deletions(-)
> 
> diff --git a/arch/Kconfig b/arch/Kconfig
> index f78c2be..ce4be89 100644
> --- a/arch/Kconfig
> +++ b/arch/Kconfig
> @@ -149,7 +149,6 @@ config HAVE_DEFAULT_NO_SPIN_MUTEXES
> 
>  config HAVE_HW_BREAKPOINT
>  	bool
> -	depends on PERF_EVENTS
> 
>  config HAVE_MIXED_BREAKPOINTS_REGS
>  	bool
> -- 

Just a thought you might want to consider...

The need to keep the ability (HAVE_HW_BREAKPOINT) and the user-choice to
enable hardware breakpoints (through HW_BREAKPOINT) in separate config
options isn't very clear to me (and is a bit confusing with very similar
names).

Why not make HAVE_HW_BREAKPOINT selectable by the user (which in turn
would turn on PERF_EVENTS) for a given architecture?

Thanks,
K.Prasad

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