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Message-ID: <1436817022.27924.74.camel@stgolabs.net>
Subject: Re: [PATCH 3/7] locking/pvqspinlock: Implement wait-early for
 overcommitted guest
From: Davidlohr Bueso <dave@stgolabs.net>
To: Waiman Long <Waiman.Long@hp.com>
Cc: Peter Zijlstra <peterz@infradead.org>, Ingo Molnar <mingo@redhat.com>,
        Thomas Gleixner <tglx@linutronix.de>, "H. Peter Anvin" <hpa@zytor.com>,
        x86@kernel.org, linux-kernel@vger.kernel.org,
        Scott J Norton <scott.norton@hp.com>,
        Douglas Hatch <doug.hatch@hp.com>
Date: Mon, 13 Jul 2015 12:50:22 -0700
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References: <1436647018-49734-1-git-send-email-Waiman.Long@hp.com>
	 <1436647018-49734-4-git-send-email-Waiman.Long@hp.com>
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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.