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x86: Make xen use the paravirt clocksource structs and functions
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This patch updates the xen guest to use the pvclock structs
and helper functions.

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Acked-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Signed-off-by: Avi Kivity <avi@qumranet.com>
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@kraxel @avikivity
kraxel authored and avikivity committed Jun 24, 2008
1 parent 7af192c commit 1c7b67f
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Showing 3 changed files with 16 additions and 124 deletions.
1 change: 1 addition & 0 deletions arch/x86/xen/Kconfig
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Original file line number Diff line number Diff line change
Expand Up @@ -5,6 +5,7 @@
config XEN
bool "Xen guest support"
select PARAVIRT
select PARAVIRT_CLOCK
depends on X86_32
depends on X86_CMPXCHG && X86_TSC && !(X86_VISWS || X86_VOYAGER)
help
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132 changes: 12 additions & 120 deletions arch/x86/xen/time.c
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Original file line number Diff line number Diff line change
Expand Up @@ -14,6 +14,7 @@
#include <linux/kernel_stat.h>
#include <linux/math64.h>

#include <asm/pvclock.h>
#include <asm/xen/hypervisor.h>
#include <asm/xen/hypercall.h>

Expand All @@ -31,17 +32,6 @@

static cycle_t xen_clocksource_read(void);

/* These are perodically updated in shared_info, and then copied here. */
struct shadow_time_info {
u64 tsc_timestamp; /* TSC at last update of time vals. */
u64 system_timestamp; /* Time, in nanosecs, since boot. */
u32 tsc_to_nsec_mul;
int tsc_shift;
u32 version;
};

static DEFINE_PER_CPU(struct shadow_time_info, shadow_time);

/* runstate info updated by Xen */
static DEFINE_PER_CPU(struct vcpu_runstate_info, runstate);

Expand Down Expand Up @@ -211,7 +201,7 @@ unsigned long long xen_sched_clock(void)
unsigned long xen_cpu_khz(void)
{
u64 xen_khz = 1000000ULL << 32;
const struct vcpu_time_info *info =
const struct pvclock_vcpu_time_info *info =
&HYPERVISOR_shared_info->vcpu_info[0].time;

do_div(xen_khz, info->tsc_to_system_mul);
Expand All @@ -223,129 +213,33 @@ unsigned long xen_cpu_khz(void)
return xen_khz;
}

/*
* Reads a consistent set of time-base values from Xen, into a shadow data
* area.
*/
static unsigned get_time_values_from_xen(void)
{
struct vcpu_time_info *src;
struct shadow_time_info *dst;

/* src is shared memory with the hypervisor, so we need to
make sure we get a consistent snapshot, even in the face of
being preempted. */
src = &__get_cpu_var(xen_vcpu)->time;
dst = &__get_cpu_var(shadow_time);

do {
dst->version = src->version;
rmb(); /* fetch version before data */
dst->tsc_timestamp = src->tsc_timestamp;
dst->system_timestamp = src->system_time;
dst->tsc_to_nsec_mul = src->tsc_to_system_mul;
dst->tsc_shift = src->tsc_shift;
rmb(); /* test version after fetching data */
} while ((src->version & 1) | (dst->version ^ src->version));

return dst->version;
}

/*
* Scale a 64-bit delta by scaling and multiplying by a 32-bit fraction,
* yielding a 64-bit result.
*/
static inline u64 scale_delta(u64 delta, u32 mul_frac, int shift)
{
u64 product;
#ifdef __i386__
u32 tmp1, tmp2;
#endif

if (shift < 0)
delta >>= -shift;
else
delta <<= shift;

#ifdef __i386__
__asm__ (
"mul %5 ; "
"mov %4,%%eax ; "
"mov %%edx,%4 ; "
"mul %5 ; "
"xor %5,%5 ; "
"add %4,%%eax ; "
"adc %5,%%edx ; "
: "=A" (product), "=r" (tmp1), "=r" (tmp2)
: "a" ((u32)delta), "1" ((u32)(delta >> 32)), "2" (mul_frac) );
#elif __x86_64__
__asm__ (
"mul %%rdx ; shrd $32,%%rdx,%%rax"
: "=a" (product) : "0" (delta), "d" ((u64)mul_frac) );
#else
#error implement me!
#endif

return product;
}

static u64 get_nsec_offset(struct shadow_time_info *shadow)
{
u64 now, delta;
now = native_read_tsc();
delta = now - shadow->tsc_timestamp;
return scale_delta(delta, shadow->tsc_to_nsec_mul, shadow->tsc_shift);
}

static cycle_t xen_clocksource_read(void)
{
struct shadow_time_info *shadow = &get_cpu_var(shadow_time);
struct pvclock_vcpu_time_info *src;
cycle_t ret;
unsigned version;

do {
version = get_time_values_from_xen();
barrier();
ret = shadow->system_timestamp + get_nsec_offset(shadow);
barrier();
} while (version != __get_cpu_var(xen_vcpu)->time.version);

put_cpu_var(shadow_time);

src = &get_cpu_var(xen_vcpu)->time;
ret = pvclock_clocksource_read(src);
put_cpu_var(xen_vcpu);
return ret;
}

static void xen_read_wallclock(struct timespec *ts)
{
const struct shared_info *s = HYPERVISOR_shared_info;
u32 version;
u64 delta;
struct timespec now;

/* get wallclock at system boot */
do {
version = s->wc_version;
rmb(); /* fetch version before time */
now.tv_sec = s->wc_sec;
now.tv_nsec = s->wc_nsec;
rmb(); /* fetch time before checking version */
} while ((s->wc_version & 1) | (version ^ s->wc_version));
struct shared_info *s = HYPERVISOR_shared_info;
struct pvclock_wall_clock *wall_clock = &(s->wc);
struct pvclock_vcpu_time_info *vcpu_time;

delta = xen_clocksource_read(); /* time since system boot */
delta += now.tv_sec * (u64)NSEC_PER_SEC + now.tv_nsec;

now.tv_nsec = do_div(delta, NSEC_PER_SEC);
now.tv_sec = delta;

set_normalized_timespec(ts, now.tv_sec, now.tv_nsec);
vcpu_time = &get_cpu_var(xen_vcpu)->time;
pvclock_read_wallclock(wall_clock, vcpu_time, ts);
put_cpu_var(xen_vcpu);
}

unsigned long xen_get_wallclock(void)
{
struct timespec ts;

xen_read_wallclock(&ts);

return ts.tv_sec;
}

Expand Down Expand Up @@ -569,8 +463,6 @@ __init void xen_time_init(void)
{
int cpu = smp_processor_id();

get_time_values_from_xen();

clocksource_register(&xen_clocksource);

if (HYPERVISOR_vcpu_op(VCPUOP_stop_periodic_timer, cpu, NULL) == 0) {
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7 changes: 3 additions & 4 deletions include/xen/interface/xen.h
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Original file line number Diff line number Diff line change
Expand Up @@ -10,6 +10,7 @@
#define __XEN_PUBLIC_XEN_H__

#include <asm/xen/interface.h>
#include <asm/pvclock-abi.h>

/*
* XEN "SYSTEM CALLS" (a.k.a. HYPERCALLS).
Expand Down Expand Up @@ -336,7 +337,7 @@ struct vcpu_info {
uint8_t evtchn_upcall_mask;
unsigned long evtchn_pending_sel;
struct arch_vcpu_info arch;
struct vcpu_time_info time;
struct pvclock_vcpu_time_info time;
}; /* 64 bytes (x86) */

/*
Expand Down Expand Up @@ -384,9 +385,7 @@ struct shared_info {
* Wallclock time: updated only by control software. Guests should base
* their gettimeofday() syscall on this wallclock-base value.
*/
uint32_t wc_version; /* Version counter: see vcpu_time_info_t. */
uint32_t wc_sec; /* Secs 00:00:00 UTC, Jan 1, 1970. */
uint32_t wc_nsec; /* Nsecs 00:00:00 UTC, Jan 1, 1970. */
struct pvclock_wall_clock wc;

struct arch_shared_info arch;

Expand Down

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