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Subject[PATCH 0/2] tracing: fix uptime overflow problem
Date
The "uptime" tracer added in:
commit 8aacf017b065a805d27467843490c976835eb4a5
tracing: Add "uptime" trace clock that uses jiffies
has wraparound problems when the system has been up more
than 1 hour 11 minutes and 34 seconds. It converts jiffies
to nanoseconds using:
(u64)jiffies_to_usecs(jiffy) * 1000ULL
but since jiffies_to_usecs() only returns a 32-bit value, it
truncates at 2^32 microseconds. An additional problem on 32-bit
systems is that the argument is "unsigned long", so fixing the
return value only helps until 2^32 jiffies (49.7 days on a HZ=1000
system).

Tony provide full featured jiffies_to_nsecs() function, but
can't resolve another problem that jiffies_lock is not safe
in NMI context.

Now we use the lockless function __current_kernel_time() and
getboottime() to calculate the uptime.

The former discussion is here:
http://lkml.org/lkml/2014/4/8/525

Additional, I changed trace_clock_jiffies to trace_clock_uptime,
in order to better describe its function and updated the document.

Xie XiuQi (2):
tracing: fix uptime overflow problem
tracing: update Documentation/trace/ftrace.txt for uptime

Documentation/trace/ftrace.txt | 3 +--
include/linux/trace_clock.h | 2 +-
kernel/trace/trace.c | 2 +-
kernel/trace/trace_clock.c | 15 +++++++++++----
4 files changed, 14 insertions(+), 8 deletions(-)

--
2.0.0



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