The patch titled
sched_clock: fix calculation of other CPU
has been removed from the -mm tree. Its filename was
sched_clock-fix-calculation-of-other-cpu.patch
This patch was dropped because it was merged into mainline or a subsystem tree
The current -mm tree may be found at http://userweb.kernel.org/~akpm/mmotm/
------------------------------------------------------
Subject: sched_clock: fix calculation of other CPU
From: Steven Rostedt <rostedt@xxxxxxxxxxx>
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 <srostedt@xxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: john stultz <johnstul@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
kernel/sched_clock.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff -puN kernel/sched_clock.c~sched_clock-fix-calculation-of-other-cpu kernel/sched_clock.c
--- a/kernel/sched_clock.c~sched_clock-fix-calculation-of-other-cpu
+++ a/kernel/sched_clock.c
@@ -160,8 +160,8 @@ 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 {
_
Patches currently in -mm which might be from rostedt@xxxxxxxxxxx are
linux-next.patch
ftrace-disable-function-tracing-bringing-up-new-cpu.patch
split-the-typecheck-macros-out-of-include-linux-kernelh.patch
locking-add-typecheck-on-irqsave-and-friends-for-correct-flags.patch
locking-add-typecheck-on-irqsave-and-friends-for-correct-flags-fix.patch
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