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

Boris Ostrovsky
2014-12-23T15:25:49Z

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