linux-kernel - Re: [PATCH v5 1/6] locking/pvqspinlock: Unconditional PV kick with _Q_SLOW

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Message-ID: <55CD4D54.2090008@hp.com>
Date:	Thu, 13 Aug 2015 22:07:16 -0400
From:	Waiman Long <waiman.long@...com>
To:	Peter Zijlstra <peterz@...radead.org>
CC:	Ingo Molnar <mingo@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
	linux-kernel@...r.kernel.org, Scott J Norton <scott.norton@...com>,
	Douglas Hatch <doug.hatch@...com>,
	Davidlohr Bueso <dave@...olabs.net>
Subject: Re: [PATCH v5 1/6] locking/pvqspinlock: Unconditional PV kick with
 _Q_SLOW_VAL

On 08/08/2015 02:02 AM, Peter Zijlstra wrote:
> On Fri, Aug 07, 2015 at 11:17:56PM -0400, Waiman Long wrote:
>> If _Q_SLOW_VAL has been set, the vCPU state must have been vcpu_hashed.
>> The extra check at the end of __pv_queued_spin_unlock() is unnecessary
>> and so is removed.
> This is half the patch it should be.
>
> Because if the load is not needed, then the store is not either, and
> then there's the comments to update.

Sorry for the late reply.


That is true. Setting state to vcpu_hashed in pv_wait_head() isn't 
really necessary. I kept it there for consistency sake as the state may 
be set to vcpu_hashed in pv_kick_node(). We can certainly take that out.

BTW, could you also review the other patches when you have time? I am 
coming to the LinuxCon/Plumbers next week. Hopefully, I can chat with 
you again.

Cheers,
Longman

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