RFR: [XS] 8228658: test GetTotalSafepointTime.java fails on fast Linux machines with Total safepoint time 0 ms

[Baesken, Matthias]

Hello  JC / David,   here is a second webrev  :

http://cr.openjdk.java.net/~mbaesken/webrevs/8228658.1/

It moves   the  thread dump execution into a  method  executeThreadDumps(long)     , and also adds  while loops   (but with a limitation  for the number of thread dumps, really don’t

 want to cause timeouts etc.).    I removed a check for  MAX_VALUE_FOR_PASS   because we cannot go over Long.MAX_VALUE .




Hope you like this version  better.



Best regards, Matthias


From: Jean Christophe Beyler <jcbeyler at google.com>
Sent: Dienstag, 30. Juli 2019 05:39
To: David Holmes <david.holmes at oracle.com>
Cc: Baesken, Matthias <matthias.baesken at sap.com>; hotspot-dev at openjdk.java.net; serviceability-dev <serviceability-dev at openjdk.java.net>
Subject: Re: RFR: [XS] 8228658: test GetTotalSafepointTime.java fails on fast Linux machines with Total safepoint time 0 ms

Hi Matthias,

I wonder if you should not do what David is suggesting and then put that whole code (the while loop) in a helper method. Below you have a calculation again using value2 (which I wonder what the added value of it is though) but anyway, that value2 could also be 0 at some point, no?

So would it not be best to just refactor the getAllStackTraces and calculate safepoint time in a helper method for both value / value2 variables?

Thanks,
Jc

On Mon, Jul 29, 2019 at 7:50 PM David Holmes <david.holmes at oracle.com<mailto:david.holmes at oracle.com>> wrote:
Hi Matthias,

On 29/07/2019 8:20 pm, Baesken, Matthias wrote:
> Hello , please review this small test fix .
>
> The test test/jdk/sun/management/HotspotRuntimeMBean/GetTotalSafepointTime.java fails sometimes on fast Linux machines with this error message :
>
> java.lang.RuntimeException: Total safepoint time illegal value: 0 ms (MIN = 1; MAX = 9223372036854775807)
>
> looks like the total safepoint time is too low currently on these machines, it is < 1 ms.
>
> There might be several ways to handle this :
>
>    *   Change the test  in a way that it might generate nigher safepoint times
>    *   Allow  safepoint time  == 0 ms
>    *   Offer an additional interface that gives  safepoint times  with finer granularity ( currently the HS has safepoint time values in ns , see  jdk/src/hotspot/share/runtime/safepoint.cpp   SafepointTracing::end
>
> But it is converted on ms in this code
>
> 114jlong RuntimeService::safepoint_time_ms() {
> 115  return UsePerfData ?
> 116    Management::ticks_to_ms(_safepoint_time_ticks->get_value()) : -1;
> 117}
>
> 064jlong Management::ticks_to_ms(jlong ticks) {
> 2065  assert(os::elapsed_frequency() > 0, "Must be non-zero");
> 2066  return (jlong)(((double)ticks / (double)os::elapsed_frequency())
> 2067                 * (double)1000.0);
> 2068}
>
>
>
> Currently I go for  the first attempt (and try to generate  higher safepoint times in my patch) .

Yes that's probably best. Coarse-grained timing on very fast machines
was bound to eventually lead to problems.

But perhaps a more future-proof approach is to just add a do-while loop
around the stack dumps and only exit when we have a non-zero safepoint
time?

Thanks,
David
-----

> Bug/webrev :
>
> https://bugs.openjdk.java.net/browse/JDK-8228658
>
> http://cr.openjdk.java.net/~mbaesken/webrevs/8228658.0/
>
>
> Thanks, Matthias
>


--

Thanks,
Jc
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://mail.openjdk.java.net/pipermail/serviceability-dev/attachments/20190730/e7685960/attachment-0001.html>