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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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1 changed files with 2 additions and 2 deletions
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@ -203,8 +203,8 @@ u64 sched_clock_cpu(int cpu)
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now -= my_scd->tick_raw;
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now += scd->tick_raw;
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now -= my_scd->tick_gtod;
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now += scd->tick_gtod;
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now += my_scd->tick_gtod;
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now -= scd->tick_gtod;
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__raw_spin_unlock(&my_scd->lock);
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} else {
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