path: root/Documentation/time_interpolators.txt
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authorLinus Torvalds <>2005-04-16 15:20:36 -0700
committerLinus Torvalds <>2005-04-16 15:20:36 -0700
commit1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 (patch)
tree0bba044c4ce775e45a88a51686b5d9f90697ea9d /Documentation/time_interpolators.txt
Initial git repository build. I'm not bothering with the full history, even though we have it. We can create a separate "historical" git archive of that later if we want to, and in the meantime it's about 3.2GB when imported into git - space that would just make the early git days unnecessarily complicated, when we don't have a lot of good infrastructure for it. Let it rip!
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+Time Interpolators
+Time interpolators are a base of time calculation between timer ticks and
+allow an accurate determination of time down to the accuracy of the time
+source in nanoseconds.
+The architecture specific code typically provides gettimeofday and
+settimeofday under Linux. The time interpolator provides both if an arch
+defines CONFIG_TIME_INTERPOLATION. The arch still must set up timer tick
+operations and call the necessary functions to advance the clock.
+With the time interpolator a standardized interface exists for time
+interpolation between ticks. The provided logic is highly scalable
+and has been tested in SMP situations of up to 512 CPUs.
+If CONFIG_TIME_INTERPOLATION is defined then the architecture specific code
+(or the device drivers - like HPET) may register time interpolators.
+These are typically defined in the following way:
+static struct time_interpolator my_interpolator {
+ .frequency = MY_FREQUENCY,
+ .source = TIME_SOURCE_MMIO32,
+ .shift = 8, /* scaling for higher accuracy */
+ .drift = -1, /* Unknown drift */
+ .jitter = 0 /* time source is stable */
+void time_init(void)
+ ....
+ /* Initialization of the timer *.
+ my_interpolator.address = &my_timer;
+ register_time_interpolator(&my_interpolator);
+ ....
+For more details see include/linux/timex.h and kernel/timer.c.
+Christoph Lameter <>, October 31, 2004