RFR(S): 8241638: launcher time metrics alway report 1 on Linux when _JAVA_LAUNCHER_DEBUG set(Internet mail)

[David Holmes]

Hi Lin,

On 31/03/2020 12:39 pm, linzang(臧琳) wrote:
> Hi David, Henry, Alan,
>      Thanks a lot for your review.
>      I have considered use clock_gettime() first, but I seached the code and found there is a marco SUPPORTS_CLOCK_MONOTONIC guard the usage of it. Which makes me think it may not be available under specific situation. So I choosed gettimeofday.
>     Do you think the patch need to be refined to remove HAVE_GETHRTIME as Alan suggested?  Thanks.

Leaving it as-is seems okay. Though the likelihood of anyone taking 
advantage of an existing gethrtime() function anywhere other than 
Solaris seems near zero. But if the Solaris port deprecation goes ahead 
the point will be moot as only the "linux" version will remain.

This comment block needs fixing up:

  37 /*
  38  *  * Add gethrtime() implementation for launch time debug on Linux.
  39  *   */

Also a nit but the new function can be called whatever you like as you 
are defining CounterGet, so calling it gethrtime() is a bit misleading - 
I suggest getTimeMicros().

Thanks,
David

> BRs,
> Lin
> 
> >On 2020/3/31, 8:05 AM, "David Holmes" <david.holmes at oracle.com> wrote:
>>
>>     On 31/03/2020 4:08 am, Henry Jen wrote:
>>     > Based on my understanding to gethrtime(), the main benefit is not to be affected by settimeofday or adjtime. I think it is probably better to use
>>     >
>>     > clock_gettime(CLOCK_MONOTONIC_RAW, ts);
>>     >
>>     > which I checked seems to be available on both Linux and Mac. Haven’t test it though.
>>     
>>     Not guaranteed to be available - either clock_gettime function or that
>>     particular clock - at build time or runtime. We use a check in the build
>>     system to determine build-time availability for hotspot, and then use
>>     dl_lookup etc at runtime to determine if actually available. We should
>>     be able to get rid of this one day but we checked fairly recently and
>>     there were still some issues.
>      
>>     gettimeofday is a lot better than returning 1. Otherwise call into the
>>     VM and use JVM_NanoTime.
>>     
>>     Cheers,
>>     David
>>     -----
>>     
>>     > Cheers,
>>     > Henry
>>     >
>>     >> On Mar 30, 2020, at 1:37 AM, Alan Bateman <Alan.Bateman at oracle.com> wrote:
>>     >>
>>     >> On 30/03/2020 03:41, linzang(臧琳) wrote:
>>     >>> Dear All,
>>     >>>       May I ask your help to reivew this tiny patch? Thanks.
>>     >>>
>>     >>>
>>     >>>
>>     >>> BRs,
>>     >>> Lin
>>     >>>
>>     >>> From: "linzang(臧琳)" <linzang at tencent.com>
>>     >>> Date: Thursday, March 26, 2020 at 3:13 PM
>>     >>> To: "core-libs-dev at openjdk.java.net" <core-libs-dev at openjdk.java.net>
>>     >>> Subject: RFR(S): 8241638: launcher time metrics alway report 1 on Linux when _JAVA_LAUNCHER_DEBUG set
>>     >>>
>>     >>> Dear All,
>>     >>> May I ask your help to review this tiny fix?
>>     >>>      Bug: https://bugs.openjdk.java.net/browse/JDK-8241638
>>     >>>      Webrev: http://cr.openjdk.java.net/~lzang/8241638/webrev01/
>>     >>> Thanks!
>>     >>>
>>     >> Using gettimeofday on non-Solaris platforms seems reasonable here. The comment in the patch suggests Linux but it's other Unix builds too. Also just a minor nit that the code in java.base uses 4-space indent, not 2. Looking at the patch makes me wondering if we should remove HAVE_GETHRTIME as it seems to be only used on Solaris >and the launcher is already using #ifdef __solaris__ in several places. Henry, do you have any comments on this?
>   >   >>
>   >   >> -Alan
>   >   >
>      
>      
>