From mboxrd@z Thu Jan  1 00:00:00 1970
From: Glauber Costa <glommer@redhat.com>
Subject: Re: [KVM timekeeping 03/35] Move TSC offset writes to common code
Date: Fri, 20 Aug 2010 14:06:43 -0300
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References: <1282291669-25709-1-git-send-email-zamsden@redhat.com>
 <1282291669-25709-4-git-send-email-zamsden@redhat.com>
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Cc: kvm@vger.kernel.org, Avi Kivity <avi@redhat.com>,
	Marcelo Tosatti <mtosatti@redhat.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	John Stultz <johnstul@us.ibm.com>, linux-kernel@vger.kernel.org
To: Zachary Amsden <zamsden@redhat.com>
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On Thu, Aug 19, 2010 at 10:07:17PM -1000, Zachary Amsden wrote:
> Also, ensure that the storing of the offset and the reading of the TSC
> are never preempted by taking a spinlock.  While the lock is overkill
> now, it is useful later in this patch series.
> 
> +	spinlock_t tsc_write_lock;
Forgive my utter ignorance, specially if it is to become
obvious in a latter patch: This is a vcpu-local operation,
uses rdtscl, so pcpu-local too, and we don't expect
multiple writers to it at the same time.

Why do we need this lock?