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authorjohn stultz <johnstul@us.ibm.com>2009-08-20 06:13:34 +0400
committerThomas Gleixner <tglx@linutronix.de>2009-08-21 23:43:46 +0400
commitda15cfdae03351c689736f8d142618592e3cebc3 (patch)
tree497fe3f77e27fa9cf0a484422c7bc382031df1bd /include/linux/time.h
parent8cab02dc3c58a12235c6d463ce684dded9696848 (diff)
downloadlinux-da15cfdae03351c689736f8d142618592e3cebc3.tar.xz
time: Introduce CLOCK_REALTIME_COARSE
After talking with some application writers who want very fast, but not fine-grained timestamps, I decided to try to implement new clock_ids to clock_gettime(): CLOCK_REALTIME_COARSE and CLOCK_MONOTONIC_COARSE which returns the time at the last tick. This is very fast as we don't have to access any hardware (which can be very painful if you're using something like the acpi_pm clocksource), and we can even use the vdso clock_gettime() method to avoid the syscall. The only trade off is you only get low-res tick grained time resolution. This isn't a new idea, I know Ingo has a patch in the -rt tree that made the vsyscall gettimeofday() return coarse grained time when the vsyscall64 sysctrl was set to 2. However this affects all applications on a system. With this method, applications can choose the proper speed/granularity trade-off for themselves. Signed-off-by: John Stultz <johnstul@us.ibm.com> Cc: Andi Kleen <andi@firstfloor.org> Cc: nikolag@ca.ibm.com Cc: Darren Hart <dvhltc@us.ibm.com> Cc: arjan@infradead.org Cc: jonathan@jonmasters.org LKML-Reference: <1250734414.6897.5.camel@localhost.localdomain> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Diffstat (limited to 'include/linux/time.h')
-rw-r--r--include/linux/time.h4
1 files changed, 4 insertions, 0 deletions
diff --git a/include/linux/time.h b/include/linux/time.h
index f505988398e6..256232f7e5e6 100644
--- a/include/linux/time.h
+++ b/include/linux/time.h
@@ -110,6 +110,8 @@ extern int timekeeping_suspended;
unsigned long get_seconds(void);
struct timespec current_kernel_time(void);
+struct timespec __current_kernel_time(void); /* does not hold xtime_lock */
+struct timespec get_monotonic_coarse(void);
#define CURRENT_TIME (current_kernel_time())
#define CURRENT_TIME_SEC ((struct timespec) { get_seconds(), 0 })
@@ -243,6 +245,8 @@ struct itimerval {
#define CLOCK_PROCESS_CPUTIME_ID 2
#define CLOCK_THREAD_CPUTIME_ID 3
#define CLOCK_MONOTONIC_RAW 4
+#define CLOCK_REALTIME_COARSE 5
+#define CLOCK_MONOTONIC_COARSE 6
/*
* The IDs of various hardware clocks: