From b9877c907d56b803b5b0241c2465ce768809fce9 Mon Sep 17 00:00:00 2001 From: Tim Schmielau Date: Wed, 13 Oct 2004 07:27:49 -0700 Subject: [PATCH] Fix reporting of process start times Derive process start times from the posix_clock_monotonic notion of uptime instead of "jiffies", consistent with the earlier change to /proc/uptime itself. (http://linus.bkbits.net:8080/linux-2.5/cset@3ef4851dGg0fxX58R9Zv8SIq9fzNmQ?na%0Av=index.html|src/.|src/fs|src/fs/proc|related/fs/proc/proc_misc.c) Process start times are reported to userspace in units of 1/USER_HZ since boot, thus applications as procps need the value of "uptime" to convert them into absolute time. Currently "uptime" is derived from an ntp-corrected time base, but process start time is derived from the free-running "jiffies" counter. This results in inaccurate, drifting process start times as seen by the user, even if the exported number stays constant, because the users notion of "jiffies" changes in time. It's John Stultz's patch anyways, which I only messed up a bit, but since people started trading signed-off lines on lkml: Signed-off-by: Tim Schmielau Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- include/linux/times.h | 20 ++++++++++++++++++++ 1 file changed, 20 insertions(+) (limited to 'include/linux/times.h') diff --git a/include/linux/times.h b/include/linux/times.h index ff00f334ffaa..0c5aa078dad4 100644 --- a/include/linux/times.h +++ b/include/linux/times.h @@ -55,6 +55,26 @@ static inline u64 jiffies_64_to_clock_t(u64 x) } #endif +static inline u64 nsec_to_clock_t(u64 x) +{ +#if (NSEC_PER_SEC % USER_HZ) == 0 + do_div(x, (NSEC_PER_SEC / USER_HZ)); +#elif (USER_HZ % 512) == 0 + x *= USER_HZ/512; + do_div(x, (NSEC_PER_SEC / 512)); +#else + /* + * max relative error 5.7e-8 (1.8s per year) for USER_HZ <= 1024, + * overflow after 64.99 years. + * exact for HZ=60, 72, 90, 120, 144, 180, 300, 600, 900, ... + */ + x *= 9; + do_div(x, (unsigned long)((9ull * NSEC_PER_SEC + (USER_HZ/2)) + / USER_HZ)); +#endif + return x; +} + struct tms { clock_t tms_utime; clock_t tms_stime; -- cgit v1.2.3