linux-kernel - Re: [PATCH v8 10/10] pvqspinlock, x86: Enable qspinlock PV support for XEN

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Date:	Wed, 02 Apr 2014 16:38:47 -0400
From:	Waiman Long <waiman.long@...com>
To:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
CC:	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Peter Zijlstra <peterz@...radead.org>,
	linux-arch@...r.kernel.org, x86@...nel.org,
	linux-kernel@...r.kernel.org,
	virtualization@...ts.linux-foundation.org,
	xen-devel@...ts.xenproject.org, kvm@...r.kernel.org,
	Paolo Bonzini <paolo.bonzini@...il.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Rik van Riel <riel@...hat.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Raghavendra K T <raghavendra.kt@...ux.vnet.ibm.com>,
	David Vrabel <david.vrabel@...rix.com>,
	Oleg Nesterov <oleg@...hat.com>,
	Gleb Natapov <gleb@...hat.com>,
	Aswin Chandramouleeswaran <aswin@...com>,
	Scott J Norton <scott.norton@...com>,
	Chegu Vinod <chegu_vinod@...com>
Subject: Re: [PATCH v8 10/10] pvqspinlock, x86: Enable qspinlock PV support
 for XEN

On 04/02/2014 10:39 AM, Konrad Rzeszutek Wilk wrote:
>> diff --git a/kernel/Kconfig.locks b/kernel/Kconfig.locks
>> index a70fdeb..451e392 100644
>> --- a/kernel/Kconfig.locks
>> +++ b/kernel/Kconfig.locks
>> @@ -229,4 +229,4 @@ config ARCH_USE_QUEUE_SPINLOCK
>>
>>   config QUEUE_SPINLOCK
>>   	def_bool y if ARCH_USE_QUEUE_SPINLOCK
>> -	depends on SMP&&  (!PARAVIRT_SPINLOCKS || !XEN)
>> +	depends on SMP
> If I read this correctly that means you cannot select any more the old
> ticketlocks? As in, if you select CONFIG_PARAVIRT on X86 it will automatically
> select ARCH_USE_QUEUE_SPINLOCK which will then enable this by default?
>
> Should the 'def_bool' be selectable?

My initial qspinlock patch allows it to be selectable, but there was 
comment that doing so would increase the testing matrix and so made it 
less desirable. That was why I made it the default for 64-bit code which 
are more likely to be used in large machines which benefit the most from 
this patch. 32-bit kernel will still use the ticket lock.

-Longman
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