Trivial patch about "Use CLOCK_MONOTONIC_RAW if available"

[David Holmes]

Hi,

On 25/01/2013 5:42 PM, liang xie wrote:
> Hi,
>
> I'm not familiar hotspot dev flow and i don't know how to make a webcr:)
> please feel free to move it to the correct list if wrong.

This list is fine. It could have gone to hotspot-runtime-dev but broder 
coverage is fine for this.

> "CLOCK_MONOTONIC_RAW" is available from 2.6.28+, it's a better choice while
> ntp
> slew happened againt CLOCK_MONOTONIC_RAW. This's important for some
> applications, e.g.  zookeeper.  Please see zookeeper--1616 for details.
>
>
> diff -r 8389681cd7b1 src/os/linux/vm/os_linux.cpp
> --- a/src/os/linux/vm/os_linux.cpp    Tue Nov 15 16:44:09 2011 -0800
> +++ b/src/os/linux/vm/os_linux.cpp    Fri Jan 25 15:14:55 2013 +0800
> @@ -1444,7 +1444,11 @@
>   jlong os::javaTimeNanos() {
>     if (Linux::supports_monotonic_clock()) {
>       struct timespec tp;
> +  #ifdef CLOCK_MONOTONIC_RAW
> +    int status = Linux::clock_gettime(CLOCK_MONOTONIC_RAW,&tp);
> +  #else
>       int status = Linux::clock_gettime(CLOCK_MONOTONIC,&tp);
> +  #endif
>       assert(status == 0, "gettime error");
>       jlong result = jlong(tp.tv_sec) * (1000 * 1000 * 1000) +
> jlong(tp.tv_nsec);
>       return result;

Unfortunately today our primary linux build platform is still at 2.6.27 
so this would have to wait until we officially update that.

But also we need to be able to run on earlier versions so this would 
have to involve a dynamic runtime check not a simple compile-time check.

I've created 8006942 to track this. It will appear on bugs.sun.com in 
the next day or so.

Thanks,
David Holmes