2014-04-09 1:32 GMT+08:00 Tony Luck <tony.l...@intel.com>:
> 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).
>
> So we provide a full featured jiffies_to_nsec() function that
> takes a "u64" argument and provides a "u64" result. To avoid
> cries of rage from the other user of this: scheduler_tick_max_deferment()
> we check whether the argument is small enough that we can do
> the calculations in 32-bit operations.
Hi Tony,
How about get uptime by get_monotonic_boottime() directly, which's
the same as /proc/uptime.
Then trace_clock_jiffies() would be like bellow:
u64 notrace trace_clock_jiffies(void)
struct timespec uptime;
get_monotonic_boottime(&uptime);
return uptime.tv_sec * NSEC_PER_SEC + uptime.tv_nsec;
}
--
XiuQi
>
> Signed-off-by: Tony Luck <tony.l...@intel.com>
> ---
> include/linux/jiffies.h | 6 +-----
> kernel/time.c | 24 ++++++++++++++++++++++++
> kernel/timeconst.bc | 12 ++++++++++++
> kernel/trace/trace_clock.c | 2 +-
> 4 files changed, 38 insertions(+), 6 deletions(-)
...
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