Re: [Xen-devel] [RFC 2/2] x86, vdso, pvclock: Simplify and speed up the vdso pvclock reader

[Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>]

On 12/23/2014 10:14 AM, Paolo Bonzini wrote:
> On 23/12/2014 16:14, Boris Ostrovsky wrote:
> > > +    do {
> > > +        version = pvti->version;
> > > +
> > > +        /* This is also a read barrier, so we'll read version first. */
> > > +        rdtsc_barrier();
> > > +        tsc = __native_read_tsc();
> > This will cause VMEXIT on Xen with TSC_MODE_ALWAYS_EMULATE which is
> > used, for example, after guest migrated (unless HW is capable of scaling
> > TSC rate).
> So does the __pvclock_read_cycles this is replacing (via
> pvclock_get_nsec_offset).
Right, I didn't notice that.

-boris

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