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 <amakhalov@vmware.com>
Acked-by: default avatarAlok 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: default avatarThomas Gleixner <tglx@linutronix.de>
parent 91d1e54e

Documentation/kernel-parameters.txt

+4 −0
Original line number Diff line number Diff line
@@ -2754,6 +2754,10 @@ bytes respectively. Such letter suffixes can also be entirely omitted. 
	no-kvmapf	[X86,KVM] Disable paravirtualized asynchronous page

			fault handling.



	no-vmw-sched-clock

			[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

			behaviour

arch/x86/kernel/cpu/vmware.c

+42 −0
Original line number Diff line number Diff line
@@ -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

#define VMWARE_HYPERVISOR_MAGIC	0x564D5868
@@ -62,10 +67,47 @@ static unsigned long vmware_get_tsc_khz(void) 
}



#ifdef CONFIG_PARAVIRT

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,

			     vmware_cyc2ns.cyc2ns_shift);

	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,

					   d->cyc2ns_shift);



	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)

{

	pv_info.name = "VMware hypervisor";

	pv_cpu_ops.io_delay = paravirt_nop;



	if (vmware_tsc_khz && vmw_sched_clock)

		vmware_sched_clock_setup();

}

#else

#define vmware_paravirt_ops_setup() do {} while (0)

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