[PATCH v3 2/2] tile: add clock_gettime support to vDSO
From: Chris Metcalf
Date: Thu Oct 02 2014 - 11:31:12 EST
This change adds support for clock_gettime with CLOCK_REALTIME
and CLOCK_MONOTONIC using vDSO. It also updates the vdso
struct nomenclature used for the clocks to match the x86 code
to keep it easier to update going forward.
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@xxxxxxxxxx>
---
arch/tile/include/asm/vdso.h | 15 ++--
arch/tile/kernel/time.c | 45 ++++++++---
arch/tile/kernel/vdso/vdso.lds.S | 2 +
arch/tile/kernel/vdso/vgettimeofday.c | 145 +++++++++++++++++++++++++++++-----
4 files changed, 172 insertions(+), 35 deletions(-)
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.
v3: rebase onto 3.17-rc7
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 2fe8323db77e..c1b362277fb7 100644
--- a/arch/tile/kernel/time.c
+++ b/arch/tile/kernel/time.c
@@ -257,21 +257,44 @@ void update_vsyscall_tz(void)
void update_vsyscall(struct timekeeper *tk)
{
- struct timespec *wtm = &tk->wall_to_monotonic;
- struct clocksource *clock = tk->tkr.clock;
-
- if (clock != &cycle_counter_cs)
+ if (tk->tkr.clock != &cycle_counter_cs)
return;
write_seqcount_begin(&vdso_data->tb_seq);
- vdso_data->xtime_tod_stamp = tk->tkr.cycle_last;
- vdso_data->xtime_clock_sec = tk->xtime_sec;
- vdso_data->xtime_clock_nsec = tk->tkr.xtime_nsec;
- vdso_data->wtom_clock_sec = wtm->tv_sec;
- vdso_data->wtom_clock_nsec = wtm->tv_nsec;
- vdso_data->mult = tk->tkr.mult;
- vdso_data->shift = tk->tkr.shift;
+ vdso_data->cycle_last = tk->tkr.cycle_last;
+ vdso_data->mask = tk->tkr.mask;
+ vdso_data->mult = tk->tkr.mult;
+ vdso_data->shift = tk->tkr.shift;
+
+ vdso_data->wall_time_sec = tk->xtime_sec;
+ vdso_data->wall_time_snsec = tk->tkr.xtime_nsec;
+
+ vdso_data->monotonic_time_sec = tk->xtime_sec
+ + tk->wall_to_monotonic.tv_sec;
+ vdso_data->monotonic_time_snsec = tk->tkr.xtime_nsec
+ + ((u64)tk->wall_to_monotonic.tv_nsec
+ << tk->tkr.shift);
+ while (vdso_data->monotonic_time_snsec >=
+ (((u64)NSEC_PER_SEC) << tk->tkr.shift)) {
+ vdso_data->monotonic_time_snsec -=
+ ((u64)NSEC_PER_SEC) << tk->tkr.shift;
+ vdso_data->monotonic_time_sec++;
+ }
+
+ vdso_data->wall_time_coarse_sec = tk->xtime_sec;
+ vdso_data->wall_time_coarse_nsec = (long)(tk->tkr.xtime_nsec >>
+ tk->tkr.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/vdso.lds.S b/arch/tile/kernel/vdso/vdso.lds.S
index 041cd6c39c83..731529f3f06f 100644
--- a/arch/tile/kernel/vdso/vdso.lds.S
+++ b/arch/tile/kernel/vdso/vdso.lds.S
@@ -82,6 +82,8 @@ VERSION
__vdso_rt_sigreturn;
__vdso_gettimeofday;
gettimeofday;
+ __vdso_clock_gettime;
+ clock_gettime;
local:*;
};
}
diff --git a/arch/tile/kernel/vdso/vgettimeofday.c b/arch/tile/kernel/vdso/vgettimeofday.c
index 7cff8fbac4f0..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)
+{
+ unsigned count;
+
+ 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)
{
- cycles_t cycles;
unsigned count;
- unsigned long sec, ns;
+
+ 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);
- sec = vdso->xtime_clock_sec;
- cycles = get_cycles() - vdso->xtime_tod_stamp;
- ns = (cycles * vdso->mult) + vdso->xtime_clock_nsec;
- ns >>= vdso->shift;
- if (ns >= NSEC_PER_SEC) {
- ns -= NSEC_PER_SEC;
- sec += 1;
- }
- } while (unlikely(read_seqcount_retry(&vdso->tb_seq, count)));
+ do_realtime(vdso, (struct timespec *)tv);
+ tv->tv_usec /= 1000;
- tv->tv_sec = sec;
- tv->tv_usec = ns / 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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