From: Steven Rostedt <rostedt@goodmis.org>
Date: Mon, 7 Jul 2008 23:49:41 +0000 (-0400)
Subject: sched_clock: fix calculation of other CPU
X-Git-Url: https://git.stricted.de/?a=commitdiff_plain;h=2b8a0cf4890d7537a77b51caa8f508e4a05a0e67;p=GitHub%2Fexynos8895%2Fandroid_kernel_samsung_universal8895.git

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 <srostedt@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: john stultz <johnstul@us.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
---

diff --git a/kernel/sched_clock.c b/kernel/sched_clock.c
index 97159e225a77..55fca1e9e12a 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 {