linux-kernel - Re: [PATCH v6 6/6] locking/pvqspinlock: Queue node adaptive spinning

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Message-ID: <20150915083804.GY16853@twins.programming.kicks-ass.net>
Date:	Tue, 15 Sep 2015 10:38:04 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Waiman Long <waiman.long@....com>
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 v6 6/6] locking/pvqspinlock: Queue node adaptive spinning

On Mon, Sep 14, 2015 at 03:37:32PM -0400, Waiman Long wrote:
> BTW, the queue head vCPU at pv_wait_head_and_lock() doesn't wait early, it
> will spin the full threshold as there is no way for it to figure out if the
> lock holder is running or not.

We can know its cpu id, right? Surely we should then be able to figure
out if its active or not, I'm thinking the KVM/Xen know these things
somewhere.
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