Re: [PATCH 1/5] Add a global synchronization point for pvclock

[Avi Kivity]

On 04/19/2010 01:43 PM, Peter Zijlstra wrote:
> > > > +
> > > >    cycle_t pvclock_clocksource_read(struct pvclock_vcpu_time_info *src)
> > > >    {
> > > >        struct pvclock_shadow_time shadow;
> > > >        unsigned version;
> > > >        cycle_t ret, offset;
> > > > +    u64 last;
> > > >
> > > >
> > > > +    do {
> > > > +        last = last_value;
> > > >          
> > > Otherwise, this assignment can see a partial update.
> > >        
> > On a 32-bit guest, that is.
> >      
> Right, do bear in mind that the x86 implementation of atomic64_read() is
> terrifyingly expensive, it is better to not do that read and simply use
> the result of the cmpxchg.
>
>    

atomic64_read() _is_ cmpxchg64b.  Are you thinking of some clever 
implementation for smp i386?

--
error compiling committee.c: too many arguments to function

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