linux-kernel - Re: [PATCH v8 00/10] qspinlock: a 4-byte queue spinlock with PV support

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Date:	Wed, 02 Apr 2014 22:10:17 -0400
From:	Waiman Long <waiman.long@...com>
To:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
CC:	Marcos Matsunaga <Marcos.Matsunaga@...cle.com>,
	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>, boris.ostrovsky@...cle.com
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 vger.kernel.org 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.

-Longman
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