linux-kernel - Re: [PATCH v4 0/3] qspinlock: Introducing a 4-byte queue spinlock

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Date:	Fri, 21 Feb 2014 09:05:27 -0800
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Waiman Long <waiman.long@...com>
Cc:	Raghavendra K T <raghavendra.kt@...ux.vnet.ibm.com>,
	Peter Zijlstra <peterz@...radead.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, Arnd Bergmann <arnd@...db.de>,
	"linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
	"the arch/x86 maintainers" <x86@...nel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Michel Lespinasse <walken@...gle.com>,
	Andi Kleen <andi@...stfloor.org>,
	Rik van Riel <riel@...hat.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	George Spelvin <linux@...izon.com>,
	Tim Chen <tim.c.chen@...ux.intel.com>,
	Daniel J Blueman <daniel@...ascale.com>,
	Alexander Fyodorov <halcy@...dex.ru>,
	Aswin Chandramouleeswaran <aswin@...com>,
	Scott J Norton <scott.norton@...com>,
	Thavatchai Makphaibulchoke <thavatchai.makpahibulchoke@...com>
Subject: Re: [PATCH v4 0/3] qspinlock: Introducing a 4-byte queue spinlock

On Fri, Feb 21, 2014 at 9:02 AM, Waiman Long <waiman.long@...com> wrote:
> On 02/20/2014 02:32 PM, Raghavendra K T wrote:
>>
>> On 02/20/2014 11:24 PM, Waiman Long wrote:
>>
>>> Now the key is how to detect if a kernel is really running in a PV
>>> environment. I need to ask some virtualization experts on that.
>>>
>>
>> For kvm you could just follow,
>> kvm_spinlock_init_jump() and KVM_FEATURE_* encoding in cpuid
>> part __do_cpuid_ent().
>>
>
> I saw that in the arch/x86/kernel/kvm.c file. So I think I can use the
> returned value of kvm_para_available() to decide if it is running in a KVM
> guest. However, I am not so sure of what to use in xen.

Just use that 'paravirt_ticketlocks_enabled' static key. Xen enables it too.

            Linus
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