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17 May 2024, 09:02:56 UTC
Revision 9dbafa5368c2b7467bd2ce034b56c54908ceb39e authored by Jan Glauber on 01 February 2006, 11:06:32 UTC, committed by Linus Torvalds on 01 February 2006, 16:53:23 UTC 
[PATCH] s390: overflow in sched_clock
 
The least significant bit of the TOD clock value returned by get_clock
is the 4096th part of a microsecond. To get to nanoseconds the value
needs to be divided by 4096 and multiplied with 1000.

The current method multiplies first and then shifts the value to make the
result as precise as possible.  The disadvantage is that the multiplication
with 1000 will overflow shortly after 52 days.  sched_clock is used by the
scheduler for time stamp deltas, if an overflow occurs between two time stamps
the scheduler will get confused.

With the patch the problem occurs only after approx.  one year, so the chance
to run into this overflow is extremly low.

Signed-off-by: Jan Glauber <jan.glauber@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
1 parent e018ba1
History
Tip revision: 9dbafa5368c2b7467bd2ce034b56c54908ceb39e authored by Jan Glauber on 01 February 2006, 11:06:32 UTC
[PATCH] s390: overflow in sched_clock
Tip revision: 9dbafa5
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