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| author | Steven Rostedt <rostedt@goodmis.org> | 2008-07-07 19:49:41 -0400 |
|---|---|---|
| committer | Ingo Molnar <mingo@elte.hu> | 2008-07-11 15:53:26 +0200 |
| commit | 2b8a0cf4890d7537a77b51caa8f508e4a05a0e67 (patch) | |
| tree | a591ef66a6340bf03e6380b6f2aa76ef2fc45ce2 /kernel | |
| parent | af52a90a14cdaa54ecbfb6e6982abb13466a4b56 (diff) | |
| download | lwn-2b8a0cf4890d7537a77b51caa8f508e4a05a0e67.tar.gz lwn-2b8a0cf4890d7537a77b51caa8f508e4a05a0e67.zip | |
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>
Diffstat (limited to 'kernel')
| -rw-r--r-- | kernel/sched_clock.c | 4 |
1 files changed, 2 insertions, 2 deletions
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 { |