linux-kernel - Re: [PATCH RFC V6 2/11] x86/ticketlock: don't inline _spin

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Date:	Wed, 21 Mar 2012 10:13:04 -0700
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Raghavendra K T <raghavendra.kt@...ux.vnet.ibm.com>
Cc:	"H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <peterz@...radead.org>,
	"the arch/x86 maintainers" <x86@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>, Avi Kivity <avi@...hat.com>,
	Marcelo Tosatti <mtosatti@...hat.com>,
	KVM <kvm@...r.kernel.org>, Andi Kleen <andi@...stfloor.org>,
	Xen Devel <xen-devel@...ts.xensource.com>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Virtualization <virtualization@...ts.linux-foundation.org>,
	Jeremy Fitzhardinge <jeremy.fitzhardinge@...rix.com>,
	Stephan Diestelhorst <stephan.diestelhorst@....com>,
	Srivatsa Vaddagiri <vatsa@...ux.vnet.ibm.com>,
	Stefano Stabellini <stefano.stabellini@...citrix.com>,
	Attilio Rao <attilio.rao@...rix.com>
Subject: Re: [PATCH RFC V6 2/11] x86/ticketlock: don't inline _spin_unlock
 when using paravirt spinlocks

On Wed, Mar 21, 2012 at 3:21 AM, Raghavendra K T
<raghavendra.kt@...ux.vnet.ibm.com> wrote:
> From: Jeremy Fitzhardinge <jeremy.fitzhardinge@...rix.com>
>
> The code size expands somewhat, and its probably better to just call
> a function rather than inline it.
>
> Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@...rix.com>
> Signed-off-by: Raghavendra K T <raghavendra.kt@...ux.vnet.ibm.com>
> ---
>  arch/x86/Kconfig     |    3 +++
>  kernel/Kconfig.locks |    2 +-
>  2 files changed, 4 insertions(+), 1 deletions(-)
> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> index 5bed94e..10c28ec 100644
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -623,6 +623,9 @@ config PARAVIRT_SPINLOCKS
>
>          If you are unsure how to answer this question, answer N.
>
> +config ARCH_NOINLINE_SPIN_UNLOCK
> +       def_bool PARAVIRT_SPINLOCKS
> +
>  config PARAVIRT_CLOCK
>        bool
>
> diff --git a/kernel/Kconfig.locks b/kernel/Kconfig.locks
> index 5068e2a..584637b 100644
> --- a/kernel/Kconfig.locks
> +++ b/kernel/Kconfig.locks
> @@ -125,7 +125,7 @@ config INLINE_SPIN_LOCK_IRQSAVE
>                 ARCH_INLINE_SPIN_LOCK_IRQSAVE
>
>  config INLINE_SPIN_UNLOCK
> -       def_bool !DEBUG_SPINLOCK && (!PREEMPT || ARCH_INLINE_SPIN_UNLOCK)
> +       def_bool !DEBUG_SPINLOCK && (!PREEMPT || ARCH_INLINE_SPIN_UNLOCK) && !ARCH_NOINLINE_SPIN_UNLOCK
>
>  config INLINE_SPIN_UNLOCK_BH
>        def_bool !DEBUG_SPINLOCK && ARCH_INLINE_SPIN_UNLOCK_BH

Ugh. This is getting really ugly.

Can we just fix it by
 - getting rid of INLINE_SPIN_UNLOCK entirely

 - replacing it with UNINLINE_SPIN_UNLOCK instead with the reverse
meaning, and no "def_bool" at all, just a simple

        config UNINLINE_SPIN_UNLOCK
                bool

 - make the various people who want to uninline the spinlocks (like
spinlock debugging, paravirt etc) all just do

        select UNINLINE_SPIN_UNLOCK

because quite frankly, the whole spinunlock inlining logic is
*already* unreadable, and you just made it worse.

                      Linus
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