linux-kernel - Re: [PATCH 3/7] locking/pvqspinlock: Implement wait-early for overcommitted guest

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Date:	Tue, 14 Jul 2015 21:39:03 -0400
From:	Waiman Long <waiman.long@...com>
To:	Davidlohr Bueso <dave@...olabs.net>
CC:	Peter Zijlstra <peterz@...radead.org>,
	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>
Subject: Re: [PATCH 3/7] locking/pvqspinlock: Implement wait-early for overcommitted
 guest

On 07/13/2015 03:50 PM, Davidlohr Bueso wrote:
> On Sat, 2015-07-11 at 16:36 -0400, Waiman Long wrote:
>>   /*
>> + * Queued Spinlock Spin Thresholds
>> + * -------------------------------
>> + * Because of the cacheline contention effect of the ticket spinlock, the
>> + * same spin threshold for queued spinlock will run a bit faster. So we set
>> + * a slight larger threshold for the queue head (1.25X) while the other queue
>> + * nodes will keep the same threshold.
> How did you come to 1.25x? These sort of magic numbers scare me.
>

Yes, this is kind of arbitrary. I am going to get rid of it in the v2 patch.

Cheers,
Longman
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