x86/vmware: Add paravirt sched clock

The default sched_clock() implementation is native_sched_clock(). It
contains code to handle non constant frequency TSCs, which creates
overhead for systems with constant frequency TSCs.

The vmware hypervisor guarantees a constant frequency TSC, so
native_sched_clock() is not required and slower than a dedicated function
which operates with one time calculated conversion factors.

Calculate the conversion factors at boot time from the tsc frequency and
install an optimized sched_clock() function via paravirt ops.

The paravirtualized clock can be disabled on the kernel command line with
the new 'no-vmw-sched-clock' option.

Signed-off-by: Alexey Makhalov <[email protected]>
Acked-by: Alok N Kataria <[email protected]>
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Thomas Gleixner <[email protected]>

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