x86/vmware: Add paravirt sched clock
authorAlexey Makhalov <amakhalov@vmware.com>
Fri, 28 Oct 2016 07:54:32 +0000 (00:54 -0700)
committerThomas Gleixner <tglx@linutronix.de>
Sun, 30 Oct 2016 07:57:08 +0000 (08:57 +0100)
commit80e9a4f21fd7ccce7e9b8439986fd028c9946dda
tree4e438295f52bacffc2ca2df175cf68c3b2722e44
parent91d1e54ebd1615d216b7f57324a5e69166a344e0
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 <amakhalov@vmware.com>
Acked-by: Alok N Kataria <akataria@vmware.com>
Cc: linux-doc@vger.kernel.org
Cc: pv-drivers@vmware.com
Cc: corbet@lwn.net
Cc: virtualization@lists.linux-foundation.org
Link: http://lkml.kernel.org/r/20161028075432.90579-4-amakhalov@vmware.com
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Documentation/kernel-parameters.txt
arch/x86/kernel/cpu/vmware.c