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x86/vmware: Add paravirt sched clock

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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>
This commit is contained in:
Alexey Makhalov 2016-10-28 00:54:32 -07:00 committed by Thomas Gleixner
parent 91d1e54ebd
commit 80e9a4f21f
2 changed files with 46 additions and 0 deletions
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4
Documentation/kernel-parameters.txt
View File

@ -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

42
arch/x86/kernel/cpu/vmware.c
View File

@ -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)