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-Tag: v2.6.27-rc1~1105^2~1^2~3
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=2b8a0cf4890d7537a77b51caa8f508e4a05a0e67;p=pandora-kernel.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>
---

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