Hi! > Two points: > 1) sigtimedwait() is unusual in that it uses the jiffies timer. Most > system call timeouts (including specifically the one in FUTEX_WAIT) > use the high-resolution timer subsystem, which is a whole different > animal with tighter guarantees, and
That is likely POSIX conformance bug, since POSIX explicitly states that sigtimedwait() shall use CLOCK_MONOTONIC to measure the timeout. "If the Monotonic Clock option is supported, the CLOCK_MONOTONIC clock shall be used to measure the time interval specified by the timeout argument." > 2) The worst-case error in tglx's proposal is 1/8 of the requested > timeout: the wakeup is after 112.5% of the requested time, plus > one tick. This is well within your requested accuracy. (For very > short timeouts, the "plus one tick" can dominate the percentage error.) Hmm, that still does not add up to the number in the original email where it says time_elapsed: 1.197057. As far as I can tell the worst case for a tick is CONFIG_HZ=100 so one tick is 0.01s and even after that we get 118.7% since we requested 1s. But that may be caused by the fact that the test uses gettimeofday() to measure the elapsed time, it should use CLOCK_MONOTONIC instead. -- Cyril Hrubis chru...@suse.cz
