RFR(xs): 8150843: [windows] os::getTimesSecs() returns negative values for kernel, user times

[David Holmes]

Hi Thomas,

On 1/03/2016 3:14 AM, Thomas Stüfe wrote:
> Hi all,
>
> please review and sponsor this small fix.
>
> It fixes an error in os::getTimesSecs() for windows which causes the
> numbers for kernel- and usertime to be off. This does not cause an error,
> because the sole user of this function, the TraceCpuTime class, uses this
> function to measure twice and calculate the deltas.
>
> I still think it is a good idea to fix this bug - with the fix, the
> returned values are based on the process start and will be the same for all
> platforms (the *nix platforms use times()).
>
> bug report: https://bugs.openjdk.java.net/browse/JDK-8150843
> webrev:
> http://cr.openjdk.java.net/~stuefe/webrevs/8150843-windows-osGetTimesSecs/webrev.00/webrev/

So the error is that kernel and user times are treated as-if they were 
absolute times - which they are not.

I still find this somewhat confusing though:

  955     jlong user_millis = jlong_from(user_time.dwHighDateTime, 
user_time.dwLowDateTime);
  956     jlong system_millis = jlong_from(kernel_time.dwHighDateTime, 
kernel_time.dwLowDateTime);


as neither of those calculations will give a value that represents 
milliseconds. I'd rather see the adjustment to millis occur above rather 
than here:

958     *process_user_time = ((double) user_millis) / ((double) (10 * 
MICROUNITS));
  959     *process_system_time = ((double) system_millis) / ((double) 
(10 * MICROUNITS));


Thanks,
David



> Kind Regards, Thomas
>