linux-kernel - Re: [PATCH] locking/pvqspinlock: Add lock holder CPU argument to pv

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Message-ID: <570F575C.8010400@linux.vnet.ibm.com>
Date:	Thu, 14 Apr 2016 16:39:56 +0800
From:	Pan Xinhui <xinhui@...ux.vnet.ibm.com>
To:	Peter Zijlstra <peterz@...radead.org>,
	Waiman Long <Waiman.Long@....com>
CC:	Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
	Scott J Norton <scott.norton@....com>,
	Douglas Hatch <doug.hatch@....com>
Subject: Re: [PATCH] locking/pvqspinlock: Add lock holder CPU argument to
 pv_wait()

On 2016年04月14日 08:21, Peter Zijlstra wrote:
> On Wed, Apr 13, 2016 at 04:59:20PM -0400, Waiman Long wrote:
>> Pan Xinhui was asking for a lock holder cpu argument in pv_wait()
>> to help the porting of pvqspinlock to PPC. The new argument will can
>> potentially help hypervisor expediate the execution of the critical
>> section so that the lock holder vCPU can release the lock sooner.
>>
>> This patch does just that by storing the previous node vCPU number.
>> In pv_wait_head_or_lock(), pv_wait() will be called with that vCPU
>> number as it is likely to be the lock holder. In pv_wait_node(),
>> -1 will be passed to pv_wait() instead to indicate that it doesn't
>> know what the current lock holder is.
> 
> Without knowing why he needs this, it is very hard to tell if this will
> suffice.
> 
> Xinhui, what do you need the extra argument for?
> 

We the could give current vcpu's slice to that vcpu. The lock holder has more slice to run, the lock might be unlocked earlier. :)