Commit 80e9a4f2 authored by Alexey Makhalov's avatar Alexey Makhalov Committed by Thomas Gleixner
Browse files

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: default avatarAlexey Makhalov <>
Acked-by: default avatarAlok N Kataria <>

Signed-off-by: default avatarThomas Gleixner <>
parent 91d1e54e
......@@ -2754,6 +2754,10 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page
fault handling.
[X86,PV_OPS] Disable paravirtualized VMware scheduler
clock and use the default one.
no-steal-acc [X86,KVM] Disable paravirtualized steal time accounting.
steal time is computed, but won't influence scheduler
......@@ -24,10 +24,15 @@
#include <linux/dmi.h>
#include <linux/init.h>
#include <linux/export.h>
#include <linux/clocksource.h>
#include <asm/div64.h>
#include <asm/x86_init.h>
#include <asm/hypervisor.h>
#include <asm/apic.h>
#include <asm/timer.h>
#undef pr_fmt
#define pr_fmt(fmt) "vmware: " fmt
#define CPUID_VMWARE_INFO_LEAF 0x40000000
......@@ -62,10 +67,47 @@ static unsigned long vmware_get_tsc_khz(void)
static struct cyc2ns_data vmware_cyc2ns __ro_after_init;
static int vmw_sched_clock __initdata = 1;
static __init int setup_vmw_sched_clock(char *s)
vmw_sched_clock = 0;
return 0;
early_param("no-vmw-sched-clock", setup_vmw_sched_clock);
static unsigned long long vmware_sched_clock(void)
unsigned long long ns;
ns = mul_u64_u32_shr(rdtsc(), vmware_cyc2ns.cyc2ns_mul,
ns -= vmware_cyc2ns.cyc2ns_offset;
return ns;
static void __init vmware_sched_clock_setup(void)
struct cyc2ns_data *d = &vmware_cyc2ns;
unsigned long long tsc_now = rdtsc();
clocks_calc_mult_shift(&d->cyc2ns_mul, &d->cyc2ns_shift,
vmware_tsc_khz, NSEC_PER_MSEC, 0);
d->cyc2ns_offset = mul_u64_u32_shr(tsc_now, d->cyc2ns_mul,
pv_time_ops.sched_clock = vmware_sched_clock;
pr_info("using sched offset of %llu ns\n", d->cyc2ns_offset);
static void __init vmware_paravirt_ops_setup(void)
{ = "VMware hypervisor";
pv_cpu_ops.io_delay = paravirt_nop;
if (vmware_tsc_khz && vmw_sched_clock)
#define vmware_paravirt_ops_setup() do {} while (0)
Markdown is supported
0% or .
You are about to add 0 people to the discussion. Proceed with caution.
Finish editing this message first!
Please register or to comment