linux-kernel - Re: [RFC -v3 PATCH 0/3] directed yield for Pause Loop Exiting

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Date:	Tue, 04 Jan 2011 07:42:15 +0100
From:	Mike Galbraith <efault@....de>
To:	Rik van Riel <riel@...hat.com>
Cc:	kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
	Avi Kiviti <avi@...hat.com>,
	Srivatsa Vaddagiri <vatsa@...ux.vnet.ibm.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Chris Wright <chrisw@...s-sol.org>
Subject: Re: [RFC -v3 PATCH 0/3] directed yield for Pause Loop Exiting

A couple questions.

On Mon, 2011-01-03 at 16:26 -0500, Rik van Riel wrote:
> When running SMP virtual machines, it is possible for one VCPU to be
> spinning on a spinlock, while the VCPU that holds the spinlock is not
> currently running, because the host scheduler preempted it to run
> something else.

Do you have any numbers?

If I were to, say, run a 256 CPU VM on my quad, would this help me get
more hackbench or whatever oomph from my (256X80386/20:) box?

> Both Intel and AMD CPUs have a feature that detects when a virtual
> CPU is spinning on a lock and will trap to the host.

Does an Intel Q6600 have this trap gizmo (iow will this do anything at
all for my little box if I were to try it out).

	-Mike

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