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

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

Right, I didn't notice that.


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