Messages in this thread Patch in this message | | | Date | Wed, 18 Jan 2006 17:51:15 +0100 | From | Heiko Carstens <> | Subject | [PATCH 2/7] s390: overflow in sched_clock. |
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From: Jan Glauber <jan.glauber@de.ibm.com>
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> ---
arch/s390/kernel/time.c | 2 +- 1 files changed, 1 insertion(+), 1 deletion(-)
diff -urpN linux-2.6/arch/s390/kernel/time.c linux-2.6-patched/arch/s390/kernel/time.c --- linux-2.6/arch/s390/kernel/time.c 2006-01-18 17:25:20.000000000 +0100 +++ linux-2.6-patched/arch/s390/kernel/time.c 2006-01-18 17:25:49.000000000 +0100 @@ -61,7 +61,7 @@ extern unsigned long wall_jiffies; */ unsigned long long sched_clock(void) { - return ((get_clock() - jiffies_timer_cc) * 1000) >> 12; + return ((get_clock() - jiffies_timer_cc) * 125) >> 9; } void tod_to_timeval(__u64 todval, struct timespec *xtime) - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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