From 81747ac6d3e846d1955edaa94dee9065e541b7d8 Mon Sep 17 00:00:00 2001 From: Justus Winter <4winter@informatik.uni-hamburg.de> Date: Mon, 7 Sep 2015 13:04:39 +0200 Subject: kern: use proper memory fences when handling the mapped time * include/mach/time_value.h (struct mapped_time_value): Adjust comment. * kern/mach_clock.c (mtime): Likewise. Also make it volatile. (update_mapped_time): Use full hardware barriers. (read_mapped_time): New macro with proper fences. (record_time_stamp, host_get_time): Use the new macro. --- kern/mach_clock.c | 33 ++++++++++++++++++--------------- 1 file changed, 18 insertions(+), 15 deletions(-) (limited to 'kern') diff --git a/kern/mach_clock.c b/kern/mach_clock.c index 2bcd232..dba2320 100644 --- a/kern/mach_clock.c +++ b/kern/mach_clock.c @@ -85,26 +85,36 @@ int bigadj = 1000000; /* adjust 10*tickadj if adjustment * This update protocol, with a check value, allows * do { * secs = mtime->seconds; + * __sync_synchronize(); * usecs = mtime->microseconds; + * __sync_synchronize(); * } while (secs != mtime->check_seconds); - * to read the time correctly. (On a multiprocessor this assumes - * that processors see each other's writes in the correct order. - * We have to insert write fence operations.) FIXME + * to read the time correctly. */ -mapped_time_value_t *mtime = 0; +volatile mapped_time_value_t *mtime = 0; #define update_mapped_time(time) \ MACRO_BEGIN \ if (mtime != 0) { \ mtime->check_seconds = (time)->seconds; \ - asm volatile("":::"memory"); \ + __sync_synchronize(); \ mtime->microseconds = (time)->microseconds; \ - asm volatile("":::"memory"); \ + __sync_synchronize(); \ mtime->seconds = (time)->seconds; \ } \ MACRO_END +#define read_mapped_time(time) \ +MACRO_BEGIN \ + do { \ + time->seconds = mtime->seconds; \ + __sync_synchronize(); \ + time->microseconds = mtime->microseconds; \ + __sync_synchronize(); \ + } while (time->seconds != mtime->check_seconds); \ +MACRO_END + decl_simple_lock_data(, timer_lock) /* lock for ... */ timer_elt_data_t timer_head; /* ordered list of timeouts */ /* (doubles as end-of-list) */ @@ -395,10 +405,7 @@ clock_boottime_update(struct time_value *new_time) void record_time_stamp (time_value_t *stamp) { - do { - stamp->seconds = mtime->seconds; - stamp->microseconds = mtime->microseconds; - } while (stamp->seconds != mtime->check_seconds); + read_mapped_time(stamp); time_value_add(stamp, &clock_boottime_offset); } @@ -425,11 +432,7 @@ host_get_time(host, current_time) if (host == HOST_NULL) return(KERN_INVALID_HOST); - do { - current_time->seconds = access_once(mtime->seconds); - current_time->microseconds = access_once(mtime->microseconds); - } while (current_time->seconds != access_once(mtime->check_seconds)); - + read_mapped_time(current_time); return (KERN_SUCCESS); } -- cgit v1.2.3