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Message-ID: <201410021530.s92FUrm1007050@farm-0039.internal.tilera.com>
Date: Thu, 2 Oct 2014 10:48:12 -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 v3 1/2] tile: switch to using seqlocks for the vDSO time code
Signed-off-by: Chris Metcalf <cmetcalf@...era.com>
---
arch/tile/include/asm/vdso.h | 5 ++--
arch/tile/kernel/time.c | 16 +++++-------
arch/tile/kernel/vdso/vgettimeofday.c | 47 +++++++++++------------------------
3 files changed, 24 insertions(+), 44 deletions(-)
v2: split apart seqlock and new functionality into separate commits
v3: rebase onto 3.17-rc7
diff --git a/arch/tile/include/asm/vdso.h b/arch/tile/include/asm/vdso.h
index 9f6a78d665fa..d64b0d58a7e9 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 */
diff --git a/arch/tile/kernel/time.c b/arch/tile/kernel/time.c
index d8fbc289e680..2fe8323db77e 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)
@@ -266,9 +263,8 @@ void update_vsyscall(struct timekeeper *tk)
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 = tk->tkr.cycle_last;
vdso_data->xtime_clock_sec = tk->xtime_sec;
vdso_data->xtime_clock_nsec = tk->tkr.xtime_nsec;
@@ -276,6 +272,6 @@ void update_vsyscall(struct timekeeper *tk)
vdso_data->wtom_clock_nsec = wtm->tv_nsec;
vdso_data->mult = tk->tkr.mult;
vdso_data->shift = tk->tkr.shift;
- smp_wmb();
- ++vdso_data->tb_update_count;
+
+ write_seqcount_end(&vdso_data->tb_seq);
}
diff --git a/arch/tile/kernel/vdso/vgettimeofday.c b/arch/tile/kernel/vdso/vgettimeofday.c
index e933fb9fbf5c..7cff8fbac4f0 100644
--- a/arch/tile/kernel/vdso/vgettimeofday.c
+++ b/arch/tile/kernel/vdso/vgettimeofday.c
@@ -53,50 +53,33 @@ inline unsigned long get_datapage(void)
int __vdso_gettimeofday(struct timeval *tv, struct timezone *tz)
{
cycles_t cycles;
- unsigned long count, sec, ns;
- volatile struct vdso_data *vdso_data;
+ unsigned count;
+ unsigned long sec, ns;
+ 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;
-
- sec = vdso_data->xtime_clock_sec;
- cycles = get_cycles() - vdso_data->xtime_tod_stamp;
- ns = (cycles * vdso_data->mult) + vdso_data->xtime_clock_nsec;
- ns >>= vdso_data->shift;
-
+ 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;
}
-
- /* Check whether updated, read again if so. */
- if (count == vdso_data->tb_update_count)
- break;
- }
+ } while (unlikely(read_seqcount_retry(&vdso->tb_seq, count)));
tv->tv_sec = sec;
tv->tv_usec = ns / 1000;
--
1.8.3.1
--
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