Re: [KVM timekeeping 03/35] Move TSC offset writes to common code

[Zachary Amsden]

On 08/20/2010 07:06 AM, Glauber Costa wrote:
> 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?
>
>    

Synchronizing access to the variables which we use to match TSC writes 
across multiple VCPUs.

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