tile: switch to using seqlocks for the vDSO time code

Signed-off-by: Chris Metcalf <cmetcalf@tilera.com>

3 files changed, 24 insertions, 44 deletions

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;