On Tue, Sep 30, 2014 at 03:29:45PM -0400, Chris Metcalf wrote:
> This change adds support for clock_gettime with CLOCK_REALTIME
> and CLOCK_MONOTONIC using vDSO. In addition, with this change
> we switch to use seqlocks instead of integer counters.
>
> 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 <[email protected]>
What rev is this based on? When I apply it to Linus latest (aad7fb916), it
fails in arch/tile/kernel/time.c and arch/tile/kernel/vdso/vgettimeofday.c
(see below)
> ---
> arch/tile/include/asm/vdso.h | 9 +-
> arch/tile/kernel/time.c | 31 ++++---
> arch/tile/kernel/vdso/vdso.lds.S | 2 +
> arch/tile/kernel/vdso/vgettimeofday.c | 166
> +++++++++++++++++++++++++---------
> 4 files changed, 153 insertions(+), 55 deletions(-)
>
> diff --git a/arch/tile/include/asm/vdso.h b/arch/tile/include/asm/vdso.h
> index 9f6a78d665fa..4527701fcead 100644
> --- a/arch/tile/include/asm/vdso.h
> +++ b/arch/tile/include/asm/vdso.h
> @@ -15,6 +15,7 @@
> #ifndef __TILE_VDSO_H__
> #define __TILE_VDSO_H__
>
> +#include <linux/seqlock.h>
> #include <linux/types.h>
>
> /*
> @@ -26,8 +27,8 @@
> */
>
> struct vdso_data {
> - __u64 tz_update_count; /* Timezone atomicity ctr */
> - __u64 tb_update_count; /* Timebase atomicity ctr */
> + 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 */
> @@ -37,6 +38,10 @@ struct vdso_data {
> __u32 shift; /* Cycle to nanosecond divisor (power of two) */
> __u32 tz_minuteswest; /* Minutes west of Greenwich */
> __u32 tz_dsttime; /* Type of dst correction */
> + __u64 xtime_clock_coarse_sec; /* Coarse kernel time */
> + __u64 xtime_clock_coarse_nsec;
> + __u64 wtom_clock_coarse_sec; /* Coarse wall to monotonic time */
> + __u64 wtom_clock_coarse_nsec;
> };
>
> extern struct vdso_data *vdso_data;
> diff --git a/arch/tile/kernel/time.c b/arch/tile/kernel/time.c
> index 462dcd0c1700..77624b38bdb9 100644
> --- a/arch/tile/kernel/time.c
> +++ b/arch/tile/kernel/time.c
> @@ -249,13 +249,10 @@ cycles_t ns2cycles(unsigned long nsecs)
>
> void update_vsyscall_tz(void)
> {
> - /* Userspace gettimeofday will spin while this value is odd. */
> - ++vdso_data->tz_update_count;
> - smp_wmb();
> + write_seqcount_begin(&vdso_data->tz_seq);
> vdso_data->tz_minuteswest = sys_tz.tz_minuteswest;
> vdso_data->tz_dsttime = sys_tz.tz_dsttime;
> - smp_wmb();
> - ++vdso_data->tz_update_count;
> + write_seqcount_end(&vdso_data->tz_seq);
> }
>
> void update_vsyscall(struct timekeeper *tk)
> @@ -263,20 +260,30 @@ void update_vsyscall(struct timekeeper *tk)
> struct timespec wall_time = tk_xtime(tk);
wall_time was removed by dc01c9fa ("tile: Convert VDSO timekeeping to the
precise mechanism"). This causes hunk to fail.
> struct timespec *wtm = &tk->wall_to_monotonic;
> struct clocksource *clock = tk->clock;
> + struct timespec ts;
>
> if (clock != &cycle_counter_cs)
> return;
>
> - /* Userspace gettimeofday will spin while this value is odd. */
> - ++vdso_data->tb_update_count;
> - smp_wmb();
> + 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;
> +
> + ts = timespec_add(wall_time, *wtm);
could you do something like
ts = timespec_add(&tk->wall_to_monotonic, wtm);
instead?
> + vdso_data->wtom_clock_sec = ts.tv_sec;
> + vdso_data->wtom_clock_nsec = ts.tv_nsec;
> +
> vdso_data->mult = clock->mult;
> vdso_data->shift = clock->shift;
> - smp_wmb();
> - ++vdso_data->tb_update_count;
> +
> + ts = __current_kernel_time();
> + vdso_data->xtime_clock_coarse_sec = ts.tv_sec;
> + vdso_data->xtime_clock_coarse_nsec = ts.tv_nsec;
> + ts = timespec_add(ts, *wtm);
> + vdso_data->wtom_clock_coarse_sec = ts.tv_sec;
> + vdso_data->wtom_clock_coarse_nsec = ts.tv_nsec;
> +
> + 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 51ec8e46f5f9..a09043492d1e 100644
> --- a/arch/tile/kernel/vdso/vgettimeofday.c
> +++ b/arch/tile/kernel/vdso/vgettimeofday.c
> @@ -15,8 +15,14 @@
> #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>
>
> +struct syscall_return_value {
> + long value;
> + long error;
> +};
> +
> #if CHIP_HAS_SPLIT_CYCLE()
> static inline cycles_t get_cycles_inline(void)
> {
> @@ -50,58 +56,136 @@ inline unsigned long get_datapage(void)
> return ret;
> }
>
> -int __vdso_gettimeofday(struct timeval *tv, struct timezone *tz)
> +static inline int do_realtime(struct vdso_data *vdso, struct timespec *ts)
> +{
> + int count;
> + cycles_t cycles;
> + unsigned long ns;
> +
> + do {
> + count = read_seqcount_begin(&vdso->tb_seq);
> + cycles = get_cycles() - vdso->xtime_tod_stamp;
> + ns = (cycles * vdso->mult) >> vdso->shift;
> + ts->tv_sec = vdso->xtime_clock_sec;
> + ts->tv_nsec = vdso->xtime_clock_nsec;
> + } while (unlikely(read_seqcount_retry(&vdso->tb_seq, count)));
> +
> + timespec_add_ns(ts, ns);
> + return 0;
> +}
> +
> +static inline int do_monotonic(struct vdso_data *vdso, struct timespec *ts)
> {
> + int count;
> cycles_t cycles;
> - unsigned long count, sec, ns;
> - volatile struct vdso_data *vdso_data;
> + unsigned long ns;
> +
> + do {
> + count = read_seqcount_begin(&vdso->tb_seq);
> + cycles = get_cycles() - vdso->xtime_tod_stamp;
> + ns = (cycles * vdso->mult) >> vdso->shift;
> + ts->tv_sec = vdso->wtom_clock_sec;
> + ts->tv_nsec = vdso->wtom_clock_nsec;
> + } while (unlikely(read_seqcount_retry(&vdso->tb_seq, count)));
> +
> + timespec_add_ns(ts, ns);
> + return 0;
> +}
> +
> +static inline int do_realtime_coarse(struct vdso_data *vdso,
> + struct timespec *ts)
> +{
> + unsigned long count;
> +
> + do {
> + count = read_seqcount_begin(&vdso->tb_seq);
> + ts->tv_sec = vdso->xtime_clock_coarse_sec;
> + ts->tv_nsec = vdso->xtime_clock_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 long count;
> +
> + do {
> + count = read_seqcount_begin(&vdso->tb_seq);
> + ts->tv_sec = vdso->wtom_clock_coarse_sec;
> + ts->tv_nsec = vdso->wtom_clock_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 long count;
> + struct vdso_data *vdso = (struct vdso_data *)get_datapage();
>
> - vdso_data = (struct vdso_data *)get_datapage();
> /* The use of the timezone is obsolete, normally tz is NULL. */
> if (unlikely(tz != NULL)) {
> - while (1) {
> - /* Spin until the update finish. */
> - count = vdso_data->tz_update_count;
> - if (count & 1)
> - continue;
> -
> - tz->tz_minuteswest = vdso_data->tz_minuteswest;
> - tz->tz_dsttime = vdso_data->tz_dsttime;
> -
> - /* Check whether updated, read again if so. */
> - if (count == vdso_data->tz_update_count)
> - break;
> - }
> + do {
> + count = read_seqcount_begin(&vdso->tz_seq);
> + tz->tz_minuteswest = vdso->tz_minuteswest;
> + tz->tz_dsttime = vdso->tz_dsttime;
> + } while (unlikely(read_seqcount_retry(&vdso->tz_seq, count)));
> }
>
> if (unlikely(tv == NULL))
> - return 0;
> -
> - while (1) {
> - /* Spin until the update finish. */
> - count = vdso_data->tb_update_count;
> - if (count & 1)
> - continue;
> -
> - cycles = (get_cycles() - vdso_data->xtime_tod_stamp);
> - ns = (cycles * vdso_data->mult) >> vdso_data->shift;
> - sec = vdso_data->xtime_clock_sec;
> - ns += vdso_data->xtime_clock_nsec;
> - if (ns >= NSEC_PER_SEC) {
> - ns -= NSEC_PER_SEC;
> - sec += 1;
> - }
> -
> - /* Check whether updated, read again if so. */
> - if (count == vdso_data->tb_update_count)
> - break;
> - }
> + return ret;
>
> - 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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--
Henrik Austad
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