git: 0b3382b863f3 - main - pvclock: Add 'struct pvclock' API
Konstantin Belousov
kib at FreeBSD.org
Sat Aug 14 12:58:14 UTC 2021
The branch main has been updated by kib:
URL: https://cgit.FreeBSD.org/src/commit/?id=0b3382b863f3195d88b99f94d5af7fe4a7b9726a
commit 0b3382b863f3195d88b99f94d5af7fe4a7b9726a
Author: Adam Fenn <adam at fenn.io>
AuthorDate: 2021-08-07 20:01:46 +0000
Commit: Konstantin Belousov <kib at FreeBSD.org>
CommitDate: 2021-08-14 12:57:54 +0000
pvclock: Add 'struct pvclock' API
Consolidate more hypervisor-agnostic functionality behind a new 'struct
pvclock' API.
This should also make it easier to subsequently add hypervisor-agnostic
vDSO timekeeping support.
Also, perform some clean-up:
- Remove 'pvclock_get_last_cycles()'; do not allow external access
to 'pvclock_last_systime' since this is not necessary.
- Consolidate/simplify wall and system time reading codepaths.
- Ensure correct ordering within wall and system time reading
codepaths via 'atomic(9)' and 'rdtsc_ordered()' rather than via
'rmb()'.
- Remove some extra newlines.
Sponsored by: Juniper Networks, Inc.
Sponsored by: Klara, Inc.
Reviewed by: kib
Differential Revision: https://reviews.freebsd.org/D31418
---
sys/x86/include/pvclock.h | 27 ++++++-
sys/x86/x86/pvclock.c | 194 ++++++++++++++++++++++++++++++++--------------
2 files changed, 160 insertions(+), 61 deletions(-)
diff --git a/sys/x86/include/pvclock.h b/sys/x86/include/pvclock.h
index 402ffed810ca..399017039dd0 100644
--- a/sys/x86/include/pvclock.h
+++ b/sys/x86/include/pvclock.h
@@ -29,6 +29,9 @@
#ifndef X86_PVCLOCK
#define X86_PVCLOCK
+#include <sys/types.h>
+#include <sys/timetc.h>
+
struct pvclock_vcpu_time_info {
uint32_t version;
uint32_t pad0;
@@ -43,17 +46,39 @@ struct pvclock_vcpu_time_info {
#define PVCLOCK_FLAG_TSC_STABLE 0x01
#define PVCLOCK_FLAG_GUEST_PASUED 0x02
+typedef struct pvclock_wall_clock *pvclock_get_wallclock_t(void *arg);
+
struct pvclock_wall_clock {
uint32_t version;
uint32_t sec;
uint32_t nsec;
};
+struct pvclock {
+ /* Public; initialized by the caller of 'pvclock_init()': */
+ pvclock_get_wallclock_t *get_wallclock;
+ void *get_wallclock_arg;
+ struct pvclock_vcpu_time_info *timeinfos;
+ bool stable_flag_supported;
+
+ /* Private; initialized by the 'pvclock' API: */
+ struct timecounter tc;
+};
+
+/*
+ * NOTE: 'pvclock_get_timecount()' and 'pvclock_get_wallclock()' are purely
+ * transitional; they should be removed after 'dev/xen/timer/timer.c' has been
+ * migrated to the 'struct pvclock' API.
+ */
void pvclock_resume(void);
-uint64_t pvclock_get_last_cycles(void);
uint64_t pvclock_tsc_freq(struct pvclock_vcpu_time_info *ti);
uint64_t pvclock_get_timecount(struct pvclock_vcpu_time_info *ti);
void pvclock_get_wallclock(struct pvclock_wall_clock *wc,
struct timespec *ts);
+void pvclock_init(struct pvclock *pvc, device_t dev,
+ const char *tc_name, int tc_quality, u_int tc_flags);
+void pvclock_gettime(struct pvclock *pvc, struct timespec *ts);
+int pvclock_destroy(struct pvclock *pvc);
+
#endif
diff --git a/sys/x86/x86/pvclock.c b/sys/x86/x86/pvclock.c
index c1e6f83b33bf..e0ad65d906b8 100644
--- a/sys/x86/x86/pvclock.c
+++ b/sys/x86/x86/pvclock.c
@@ -31,31 +31,34 @@ __FBSDID("$FreeBSD$");
#include <sys/param.h>
#include <sys/systm.h>
+#include <sys/clock.h>
+#include <sys/limits.h>
#include <sys/proc.h>
-#include <machine/cpufunc.h>
-#include <machine/cpu.h>
#include <machine/atomic.h>
+#include <machine/md_var.h>
#include <machine/pvclock.h>
/*
- * Last time; this guarantees a monotonically increasing clock for when
- * a stable TSC is not provided.
+ * Last system time. This is used to guarantee a monotonically non-decreasing
+ * clock for the kernel codepath and approximate the same for the vDSO codepath.
+ * In theory, this should be unnecessary absent hypervisor bug(s) and/or what
+ * should be rare cases where TSC jitter may still be visible despite the
+ * hypervisor's best efforts.
*/
-static volatile uint64_t pvclock_last_cycles;
+static volatile uint64_t pvclock_last_systime;
+
+static uint64_t pvclock_getsystime(struct pvclock *pvc);
+static void pvclock_read_time_info(
+ struct pvclock_vcpu_time_info *ti, uint64_t *ns, uint8_t *flags);
+static void pvclock_read_wall_clock(struct pvclock_wall_clock *wc,
+ struct timespec *ts);
+static u_int pvclock_tc_get_timecount(struct timecounter *tc);
void
pvclock_resume(void)
{
-
- atomic_store_rel_64(&pvclock_last_cycles, 0);
-}
-
-uint64_t
-pvclock_get_last_cycles(void)
-{
-
- return (atomic_load_acq_64(&pvclock_last_cycles));
+ atomic_store_rel_64(&pvclock_last_systime, 0);
}
uint64_t
@@ -64,12 +67,10 @@ pvclock_tsc_freq(struct pvclock_vcpu_time_info *ti)
uint64_t freq;
freq = (1000000000ULL << 32) / ti->tsc_to_system_mul;
-
if (ti->tsc_shift < 0)
freq <<= -ti->tsc_shift;
else
freq >>= ti->tsc_shift;
-
return (freq);
}
@@ -86,7 +87,6 @@ pvclock_scale_delta(uint64_t delta, uint32_t mul_frac, int shift)
delta >>= -shift;
else
delta <<= shift;
-
#if defined(__i386__)
{
uint32_t tmp1, tmp2;
@@ -122,82 +122,156 @@ pvclock_scale_delta(uint64_t delta, uint32_t mul_frac, int shift)
#else
#error "pvclock: unsupported x86 architecture?"
#endif
-
return (product);
}
-static uint64_t
-pvclock_get_nsec_offset(struct pvclock_vcpu_time_info *ti)
-{
- uint64_t delta;
-
- delta = rdtsc() - ti->tsc_timestamp;
-
- return (pvclock_scale_delta(delta, ti->tsc_to_system_mul,
- ti->tsc_shift));
-}
-
static void
pvclock_read_time_info(struct pvclock_vcpu_time_info *ti,
- uint64_t *cycles, uint8_t *flags)
+ uint64_t *ns, uint8_t *flags)
{
+ uint64_t delta;
uint32_t version;
do {
- version = ti->version;
- rmb();
- *cycles = ti->system_time + pvclock_get_nsec_offset(ti);
+ version = atomic_load_acq_32(&ti->version);
+ delta = rdtsc_ordered() - ti->tsc_timestamp;
+ *ns = ti->system_time + pvclock_scale_delta(delta,
+ ti->tsc_to_system_mul, ti->tsc_shift);
*flags = ti->flags;
- rmb();
+ atomic_thread_fence_acq();
} while ((ti->version & 1) != 0 || ti->version != version);
}
static void
-pvclock_read_wall_clock(struct pvclock_wall_clock *wc, uint32_t *sec,
- uint32_t *nsec)
+pvclock_read_wall_clock(struct pvclock_wall_clock *wc, struct timespec *ts)
{
uint32_t version;
do {
- version = wc->version;
- rmb();
- *sec = wc->sec;
- *nsec = wc->nsec;
- rmb();
+ version = atomic_load_acq_32(&wc->version);
+ ts->tv_sec = wc->sec;
+ ts->tv_nsec = wc->nsec;
+ atomic_thread_fence_acq();
} while ((wc->version & 1) != 0 || wc->version != version);
}
+static uint64_t
+pvclock_getsystime(struct pvclock *pvc)
+{
+ uint64_t now, last, ret;
+ uint8_t flags;
+
+ critical_enter();
+ pvclock_read_time_info(&pvc->timeinfos[curcpu], &now, &flags);
+ ret = now;
+ if ((flags & PVCLOCK_FLAG_TSC_STABLE) == 0) {
+ last = atomic_load_acq_64(&pvclock_last_systime);
+ do {
+ if (last > now) {
+ ret = last;
+ break;
+ }
+ } while (!atomic_fcmpset_rel_64(&pvclock_last_systime, &last,
+ now));
+ }
+ critical_exit();
+ return (ret);
+}
+
+/*
+ * NOTE: Transitional-only; this should be removed after 'dev/xen/timer/timer.c'
+ * has been migrated to the 'struct pvclock' API.
+ */
uint64_t
pvclock_get_timecount(struct pvclock_vcpu_time_info *ti)
{
- uint64_t now, last;
+ uint64_t now, last, ret;
uint8_t flags;
pvclock_read_time_info(ti, &now, &flags);
+ ret = now;
+ if ((flags & PVCLOCK_FLAG_TSC_STABLE) == 0) {
+ last = atomic_load_acq_64(&pvclock_last_systime);
+ do {
+ if (last > now) {
+ ret = last;
+ break;
+ }
+ } while (!atomic_fcmpset_rel_64(&pvclock_last_systime, &last,
+ now));
+ }
+ return (ret);
+}
- if (flags & PVCLOCK_FLAG_TSC_STABLE)
- return (now);
+/*
+ * NOTE: Transitional-only; this should be removed after 'dev/xen/timer/timer.c'
+ * has been migrated to the 'struct pvclock' API.
+ */
+void
+pvclock_get_wallclock(struct pvclock_wall_clock *wc, struct timespec *ts)
+{
+ pvclock_read_wall_clock(wc, ts);
+}
- /*
- * Enforce a monotonically increasing clock time across all VCPUs.
- * If our time is too old, use the last time and return. Otherwise,
- * try to update the last time.
- */
- do {
- last = atomic_load_acq_64(&pvclock_last_cycles);
- if (last > now)
- return (last);
- } while (!atomic_cmpset_64(&pvclock_last_cycles, last, now));
+static u_int
+pvclock_tc_get_timecount(struct timecounter *tc)
+{
+ struct pvclock *pvc = tc->tc_priv;
- return (now);
+ return (pvclock_getsystime(pvc) & UINT_MAX);
}
void
-pvclock_get_wallclock(struct pvclock_wall_clock *wc, struct timespec *ts)
+pvclock_gettime(struct pvclock *pvc, struct timespec *ts)
{
- uint32_t sec, nsec;
+ struct timespec system_ts;
+ uint64_t system_ns;
+
+ pvclock_read_wall_clock(pvc->get_wallclock(pvc->get_wallclock_arg), ts);
+ system_ns = pvclock_getsystime(pvc);
+ system_ts.tv_sec = system_ns / 1000000000ULL;
+ system_ts.tv_nsec = system_ns % 1000000000ULL;
+ timespecadd(ts, &system_ts, ts);
+}
- pvclock_read_wall_clock(wc, &sec, &nsec);
- ts->tv_sec = sec;
- ts->tv_nsec = nsec;
+void
+pvclock_init(struct pvclock *pvc, device_t dev, const char *tc_name,
+ int tc_quality, u_int tc_flags)
+{
+ KASSERT(((uintptr_t)pvc->timeinfos & PAGE_MASK) == 0,
+ ("Specified time info page(s) address is not page-aligned."));
+
+ /* Set up timecounter and timecounter-supporting members: */
+ pvc->tc.tc_get_timecount = pvclock_tc_get_timecount;
+ pvc->tc.tc_poll_pps = NULL;
+ pvc->tc.tc_counter_mask = ~0U;
+ pvc->tc.tc_frequency = 1000000000ULL;
+ pvc->tc.tc_name = tc_name;
+ pvc->tc.tc_quality = tc_quality;
+ pvc->tc.tc_flags = tc_flags;
+ pvc->tc.tc_priv = pvc;
+ pvc->tc.tc_fill_vdso_timehands = NULL;
+#ifdef COMPAT_FREEBSD32
+ pvc->tc.tc_fill_vdso_timehands32 = NULL;
+#endif
+
+ /* Register timecounter: */
+ tc_init(&pvc->tc);
+
+ /*
+ * Register wallclock:
+ * The RTC registration API expects a resolution in microseconds;
+ * pvclock's 1ns resolution is rounded up to 1us.
+ */
+ clock_register(dev, 1);
+}
+
+int
+pvclock_destroy(struct pvclock *pvc)
+{
+ /*
+ * Not currently possible since there is no teardown counterpart of
+ * 'tc_init()'.
+ */
+ return (EBUSY);
}
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