linux-kernel - Re: [PATCH] arm64: add HAVE_LATENCYTOP

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Date:	Tue, 10 Nov 2015 12:01:45 +0100
From:	Heiko Carstens <heiko.carstens@...ibm.com>
To:	Will Deacon <will.deacon@....com>
Cc:	yalin wang <yalin.wang2010@...il.com>,
	Catalin Marinas <catalin.marinas@....com>,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] arm64: add HAVE_LATENCYTOP_SUPPORT config

On Tue, Nov 10, 2015 at 10:05:48AM +0000, Will Deacon wrote:
> Hi Heiko,
> 
> On Tue, Nov 10, 2015 at 08:41:24AM +0100, Heiko Carstens wrote:
> > On Fri, Nov 06, 2015 at 04:21:10PM +0000, Will Deacon wrote:
> > > On Sat, Nov 07, 2015 at 12:11:16AM +0800, yalin wang wrote:
> > > > i just enable it on ARM64,
> > > > and it can work,
> > > > i don’t see some special requirement to enable this config .
> > > 
> > > Right, so why does HAVE_LATENCYTOP_SUPPORT exist?
[...]
> > And looking through the kernel there is at least avr32 which would break
> > at build time if the config option would be removed completely.
> > 
> > So.. renaming it to STACKTRACE_TSK_SUPPORT would be a good idea.
> 
> ftrace has a similar issue and solves it by having architectures define
> a `config STACKTRACE_SUPPORT' symbol. Over in kernel/trace/Kconfig,
> there's a `select STACKTRACE if STACKTRACE_SUPPORT', which means
> that kernel/stacktrace.c gets built and a dummy (weak symbol) version of
> save_stack_trace_tsk appears.

Ah, I wasn't aware of the weak symbol.

> I don't think adding another STACKTRACE-related Kconfig option is
> necessarily the best thing to do. Maybe we should instead have LATENCYTOP
> depend on STACKTRACE_SUPPORT (already the case) and select STACKTRACE?

LATENCYTOP also already selects STACKTRACE. So it looks like
HAVE_LATENCYTOP_SUPPORT could simply be removed.

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