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

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Date:	Thu, 22 Mar 2012 15:36:42 +0530
From:	Raghavendra K T <raghavendra.kt@...ux.vnet.ibm.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
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 03/21/2012 10:43 PM, Linus Torvalds wrote:
> 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.
>

Agree that it had become longer.

> 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

I just posted  https://lkml.org/lkml/2012/3/22/94. Please let me know
if that looks better.
And this patch should now become something like
---
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 5bed94e..2666b7d 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -613,6 +613,7 @@ config PARAVIRT
  config PARAVIRT_SPINLOCKS
	 bool "Paravirtualization layer for spinlocks"
	 depends on PARAVIRT && SMP && EXPERIMENTAL
+	 select UNINLINE_SPIN_UNLOCK
	 ---help---
	   Paravirtualized spinlocks allow a pvops backend to replace the
	   spinlock implementation with something virtualization-friendly

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