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Date: Wed, 1 Oct 2014 17:02:08 -0400
From: Chris Metcalf <cmetcalf@...era.com>
To: <linux-kernel@...r.kernel.org>,
Thomas Gleixner <tglx@...utronix.de>,
John Stultz <john.stultz@...aro.org>,
Henrik Austad <henrik@...tad.us>
Subject: [PATCH v2 2/2] tile: add clock_gettime support to vDSO
This change adds support for clock_gettime with CLOCK_REALTIME
and CLOCK_MONOTONIC using vDSO. It also updates the algorithm
used for the clocks to support sub-nanosecond times, using the
x86 architecture code as a model.
We also support the *_COARSE clockid_t, for apps that want speed
but aren't concerned about fine-grained timestamps; this saves
about 20 cycles per call (see http://lwn.net/Articles/342018/).
Signed-off-by: Chris Metcalf <cmetcalf@...era.com>
---
v2: use the x86 code as a model to address both John Stultz's
observation about sub-nanosecond updates, as well as to address
Thomas Gleixner's observation about minimizing time spent with
the seqlock held. Note that I kept the "unlikely" that Thomas
doubted would help, just for parallelism with the x86 code.
arch/tile/include/asm/vdso.h | 15 ++--
arch/tile/kernel/time.c | 45 ++++++++---
arch/tile/kernel/vdso/vgettimeofday.c | 145 +++++++++++++++++++++++++++++-----
3 files changed, 170 insertions(+), 36 deletions(-)
diff --git a/arch/tile/include/asm/vdso.h b/arch/tile/include/asm/vdso.h
index d64b0d58a7e9..9b069692153f 100644
--- a/arch/tile/include/asm/vdso.h
+++ b/arch/tile/include/asm/vdso.h
@@ -29,13 +29,18 @@
struct vdso_data {
seqcount_t tz_seq; /* Timezone seqlock */
seqcount_t tb_seq; /* Timebase seqlock */
- __u64 xtime_tod_stamp; /* TOD clock for xtime */
- __u64 xtime_clock_sec; /* Kernel time second */
- __u64 xtime_clock_nsec; /* Kernel time nanosecond */
- __u64 wtom_clock_sec; /* Wall to monotonic clock second */
- __u64 wtom_clock_nsec; /* Wall to monotonic clock nanosecond */
+ __u64 cycle_last; /* TOD clock for xtime */
+ __u64 mask; /* Cycle mask */
__u32 mult; /* Cycle to nanosecond multiplier */
__u32 shift; /* Cycle to nanosecond divisor (power of two) */
+ __u64 wall_time_sec;
+ __u64 wall_time_snsec;
+ __u64 monotonic_time_sec;
+ __u64 monotonic_time_snsec;
+ __u64 wall_time_coarse_sec;
+ __u64 wall_time_coarse_nsec;
+ __u64 monotonic_time_coarse_sec;
+ __u64 monotonic_time_coarse_nsec;
__u32 tz_minuteswest; /* Minutes west of Greenwich */
__u32 tz_dsttime; /* Type of dst correction */
};
diff --git a/arch/tile/kernel/time.c b/arch/tile/kernel/time.c
index 0661045f718d..2fdf4ebdb30e 100644
--- a/arch/tile/kernel/time.c
+++ b/arch/tile/kernel/time.c
@@ -257,22 +257,43 @@ void update_vsyscall_tz(void)
void update_vsyscall(struct timekeeper *tk)
{
- struct timespec wall_time = tk_xtime(tk);
- struct timespec *wtm = &tk->wall_to_monotonic;
- struct clocksource *clock = tk->clock;
-
- if (clock != &cycle_counter_cs)
+ if (tk->clock != &cycle_counter_cs)
return;
write_seqcount_begin(&vdso_data->tb_seq);
- vdso_data->xtime_tod_stamp = clock->cycle_last;
- vdso_data->xtime_clock_sec = wall_time.tv_sec;
- vdso_data->xtime_clock_nsec = wall_time.tv_nsec;
- vdso_data->wtom_clock_sec = wtm->tv_sec;
- vdso_data->wtom_clock_nsec = wtm->tv_nsec;
- vdso_data->mult = clock->mult;
- vdso_data->shift = clock->shift;
+ vdso_data->cycle_last = tk->clock->cycle_last;
+ vdso_data->mask = tk->clock->mask;
+ vdso_data->mult = tk->mult;
+ vdso_data->shift = tk->shift;
+
+ vdso_data->wall_time_sec = tk->xtime_sec;
+ vdso_data->wall_time_snsec = tk->xtime_nsec;
+
+ vdso_data->monotonic_time_sec = tk->xtime_sec
+ + tk->wall_to_monotonic.tv_sec;
+ vdso_data->monotonic_time_snsec = tk->xtime_nsec
+ + ((u64)tk->wall_to_monotonic.tv_nsec
+ << tk->shift);
+ while (vdso_data->monotonic_time_snsec >=
+ (((u64)NSEC_PER_SEC) << tk->shift)) {
+ vdso_data->monotonic_time_snsec -=
+ ((u64)NSEC_PER_SEC) << tk->shift;
+ vdso_data->monotonic_time_sec++;
+ }
+
+ vdso_data->wall_time_coarse_sec = tk->xtime_sec;
+ vdso_data->wall_time_coarse_nsec = (long)(tk->xtime_nsec >> tk->shift);
+
+ vdso_data->monotonic_time_coarse_sec =
+ vdso_data->wall_time_coarse_sec + tk->wall_to_monotonic.tv_sec;
+ vdso_data->monotonic_time_coarse_nsec =
+ vdso_data->wall_time_coarse_nsec + tk->wall_to_monotonic.tv_nsec;
+
+ while (vdso_data->monotonic_time_coarse_nsec >= NSEC_PER_SEC) {
+ vdso_data->monotonic_time_coarse_nsec -= NSEC_PER_SEC;
+ vdso_data->monotonic_time_coarse_sec++;
+ }
write_seqcount_end(&vdso_data->tb_seq);
}
diff --git a/arch/tile/kernel/vdso/vgettimeofday.c b/arch/tile/kernel/vdso/vgettimeofday.c
index efd00165d654..8bb21eda07d8 100644
--- a/arch/tile/kernel/vdso/vgettimeofday.c
+++ b/arch/tile/kernel/vdso/vgettimeofday.c
@@ -15,6 +15,7 @@
#define VDSO_BUILD /* avoid some shift warnings for -m32 in <asm/page.h> */
#include <linux/time.h>
#include <asm/timex.h>
+#include <asm/unistd.h>
#include <asm/vdso.h>
#if CHIP_HAS_SPLIT_CYCLE()
@@ -35,6 +36,11 @@ static inline cycles_t get_cycles_inline(void)
#define get_cycles get_cycles_inline
#endif
+struct syscall_return_value {
+ long value;
+ long error;
+};
+
/*
* Find out the vDSO data page address in the process address space.
*/
@@ -50,11 +56,82 @@ inline unsigned long get_datapage(void)
return ret;
}
-int __vdso_gettimeofday(struct timeval *tv, struct timezone *tz)
+static inline u64 vgetsns(struct vdso_data *vdso)
+{
+ return ((get_cycles() - vdso->cycle_last) & vdso->mask) * vdso->mult;
+}
+
+static inline int do_realtime(struct vdso_data *vdso, struct timespec *ts)
+{
+ unsigned count;
+ u64 ns;
+
+ do {
+ count = read_seqcount_begin(&vdso->tb_seq);
+ ts->tv_sec = vdso->wall_time_sec;
+ ns = vdso->wall_time_snsec;
+ ns += vgetsns(vdso);
+ ns >>= vdso->shift;
+ } while (unlikely(read_seqcount_retry(&vdso->tb_seq, count)));
+
+ ts->tv_sec += __iter_div_u64_rem(ns, NSEC_PER_SEC, &ns);
+ ts->tv_nsec = ns;
+
+ return 0;
+}
+
+static inline int do_monotonic(struct vdso_data *vdso, struct timespec *ts)
+{
+ unsigned count;
+ u64 ns;
+
+ do {
+ count = read_seqcount_begin(&vdso->tb_seq);
+ ts->tv_sec = vdso->monotonic_time_sec;
+ ns = vdso->monotonic_time_snsec;
+ ns += vgetsns(vdso);
+ ns >>= vdso->shift;
+ } while (unlikely(read_seqcount_retry(&vdso->tb_seq, count)));
+
+ ts->tv_sec += __iter_div_u64_rem(ns, NSEC_PER_SEC, &ns);
+ ts->tv_nsec = ns;
+
+ return 0;
+}
+
+static inline int do_realtime_coarse(struct vdso_data *vdso,
+ struct timespec *ts)
{
- cycles_t cycles;
unsigned count;
- unsigned long sec, ns;
+
+ do {
+ count = read_seqcount_begin(&vdso->tb_seq);
+ ts->tv_sec = vdso->wall_time_coarse_sec;
+ ts->tv_nsec = vdso->wall_time_coarse_nsec;
+ } while (unlikely(read_seqcount_retry(&vdso->tb_seq, count)));
+
+ return 0;
+}
+
+static inline int do_monotonic_coarse(struct vdso_data *vdso,
+ struct timespec *ts)
+{
+ unsigned count;
+
+ do {
+ count = read_seqcount_begin(&vdso->tb_seq);
+ ts->tv_sec = vdso->monotonic_time_coarse_sec;
+ ts->tv_nsec = vdso->monotonic_time_coarse_nsec;
+ } while (unlikely(read_seqcount_retry(&vdso->tb_seq, count)));
+
+ return 0;
+}
+
+struct syscall_return_value __vdso_gettimeofday(struct timeval *tv,
+ struct timezone *tz)
+{
+ struct syscall_return_value ret = { 0, 0 };
+ unsigned count;
struct vdso_data *vdso = (struct vdso_data *)get_datapage();
/* The use of the timezone is obsolete, normally tz is NULL. */
@@ -67,25 +144,55 @@ int __vdso_gettimeofday(struct timeval *tv, struct timezone *tz)
}
if (unlikely(tv == NULL))
- return 0;
+ return ret;
- do {
- count = read_seqcount_begin(&vdso->tb_seq);
- cycles = (get_cycles() - vdso->xtime_tod_stamp);
- ns = (cycles * vdso->mult) >> vdso->shift;
- sec = vdso->xtime_clock_sec;
- ns += vdso->xtime_clock_nsec;
- if (ns >= NSEC_PER_SEC) {
- ns -= NSEC_PER_SEC;
- sec += 1;
- }
- } while (unlikely(read_seqcount_retry(&vdso->tb_seq, count)));
-
- tv->tv_sec = sec;
- tv->tv_usec = ns / 1000;
+ do_realtime(vdso, (struct timespec *)tv);
+ tv->tv_usec /= 1000;
- return 0;
+ return ret;
}
int gettimeofday(struct timeval *tv, struct timezone *tz)
__attribute__((weak, alias("__vdso_gettimeofday")));
+
+static struct syscall_return_value vdso_fallback_gettime(long clock,
+ struct timespec *ts)
+{
+ struct syscall_return_value ret;
+ __asm__ __volatile__ (
+ "swint1"
+ : "=R00" (ret.value), "=R01" (ret.error)
+ : "R10" (__NR_clock_gettime), "R00" (clock), "R01" (ts)
+ : "r2", "r3", "r4", "r5", "r6", "r7",
+ "r8", "r9", "r11", "r12", "r13", "r14", "r15",
+ "r16", "r17", "r18", "r19", "r20", "r21", "r22", "r23",
+ "r24", "r25", "r26", "r27", "r28", "r29", "memory");
+ return ret;
+}
+
+struct syscall_return_value __vdso_clock_gettime(clockid_t clock,
+ struct timespec *ts)
+{
+ struct vdso_data *vdso = (struct vdso_data *)get_datapage();
+ struct syscall_return_value ret = { 0, 0 };
+
+ switch (clock) {
+ case CLOCK_REALTIME:
+ do_realtime(vdso, ts);
+ return ret;
+ case CLOCK_MONOTONIC:
+ do_monotonic(vdso, ts);
+ return ret;
+ case CLOCK_REALTIME_COARSE:
+ do_realtime_coarse(vdso, ts);
+ return ret;
+ case CLOCK_MONOTONIC_COARSE:
+ do_monotonic_coarse(vdso, ts);
+ return ret;
+ default:
+ return vdso_fallback_gettime(clock, ts);
+ }
+}
+
+int clock_gettime(clockid_t clock, struct timespec *ts)
+ __attribute__((weak, alias("__vdso_clock_gettime")));
--
1.8.3.1
--
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