From 2b8a0cf4890d7537a77b51caa8f508e4a05a0e67 Mon Sep 17 00:00:00 2001 From: Steven Rostedt Date: Mon, 7 Jul 2008 19:49:41 -0400 Subject: [PATCH] sched_clock: fix calculation of other CPU The algorithm to calculate the 'now' of another CPU is not correct. At each scheduler tick, each CPU records the last sched_clock and gtod (tick_raw and tick_gtod respectively). If the TSC is somewhat the same in speed between two clocks the algorithm would be: tick_gtod1 + (now1 - tick_raw1) = tick_gtod2 + (now2 - tick_raw2) To calculate now2 we would have: now2 = (tick_gtod1 - tick_gtod2) + (tick_raw2 - tick_raw1) + now1 Currently the algorithm is: now2 = (tick_gtod1 - tick_gtod2) + (tick_raw1 - tick_raw2) + now1 This solves most of the rest of the issues I've had with timestamps in ftace. Signed-off-by: Steven Rostedt Cc: Andrew Morton Cc: john stultz Cc: Peter Zijlstra Signed-off-by: Ingo Molnar --- kernel/sched_clock.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/kernel/sched_clock.c b/kernel/sched_clock.c index 97159e2..55fca1e 100644 --- a/kernel/sched_clock.c +++ b/kernel/sched_clock.c @@ -203,8 +203,8 @@ u64 sched_clock_cpu(int cpu) now -= my_scd->tick_raw; now += scd->tick_raw; - now -= my_scd->tick_gtod; - now += scd->tick_gtod; + now += my_scd->tick_gtod; + now -= scd->tick_gtod; __raw_spin_unlock(&my_scd->lock); } else { -- 2.7.4