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Date:	Wed, 02 Apr 2014 22:10:17 -0400
From:	Waiman Long <>
To:	Konrad Rzeszutek Wilk <>
CC:	Marcos Matsunaga <>,
	Thomas Gleixner <>,
	Ingo Molnar <>,
	"H. Peter Anvin" <>,
	Peter Zijlstra <>,,,,,,,
	Paolo Bonzini <>,
	"Paul E. McKenney" <>,
	Rik van Riel <>,
	Linus Torvalds <>,
	Raghavendra K T <>,
	David Vrabel <>,
	Oleg Nesterov <>,
	Gleb Natapov <>,
	Aswin Chandramouleeswaran <>,
	Scott J Norton <>,
	Chegu Vinod <>,
Subject: Re: [PATCH v8 00/10] qspinlock: a 4-byte queue spinlock with PV support

On 04/02/2014 04:35 PM, Waiman Long wrote:
> On 04/02/2014 10:32 AM, Konrad Rzeszutek Wilk wrote:
>> On Wed, Apr 02, 2014 at 09:27:29AM -0400, Waiman Long wrote:
>>> N.B. Sorry for the duplicate. This patch series were resent as the
>>>       original one was rejected by the list server
>>>       due to long header. There is no change in content.
>>> v7->v8:
>>>    - Remove one unneeded atomic operation from the slowpath, thus
>>>      improving performance.
>>>    - Simplify some of the codes and add more comments.
>>>    - Test for X86_FEATURE_HYPERVISOR CPU feature bit to enable/disable
>>>      unfair lock.
>>>    - Reduce unfair lock slowpath lock stealing frequency depending
>>>      on its distance from the queue head.
>>>    - Add performance data for IvyBridge-EX CPU.
>> FYI, your v7 patch with 32 VCPUs (on a 32 cpu socket machine) on an
>> HVM guest under Xen after a while stops working. The workload
>> is doing 'make -j32' on the Linux kernel.
>> Completely unresponsive. Thoughts?
> Thank for reporting that. I haven't done that much testing on Xen. My 
> focus was in KVM. I will perform more test on Xen to see if I can 
> reproduce the problem.

BTW, does the halting and sending IPI mechanism work in HVM? I saw that 
in RHEL7, PV spinlock was explicitly disabled when in HVM mode. However, 
this piece of code isn't in upstream code. So I wonder if there is 
problem with that.

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