[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

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
pvclock_get_nsec_offset).

Right, I didn't notice that.

-boris

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
http://lists.xen.org/xen-devel


 


Rackspace

Lists.xenproject.org is hosted with RackSpace, monitoring our
servers 24x7x365 and backed by RackSpace's Fanatical Support®.