RFR: 8248266: ZGC: TestUncommit.java fails due to "Exception: Uncommitted too fast" again

[Per Liden]

Hi!

Most people are back from vacations now (including myself), so I'm 
giving this thread a bump as I'm still looking for reviews on this change.

cheers,
Per

On 6/26/20 3:28 PM, Per Liden wrote:
> Hi,
> 
> The test gc/z/TestUncommit.java sometimes fail because of bad timing, 
> caused by what appears to be an heavily loaded machine so the test 
> thread doesn't get to execute in a timely manner.
> 
> I've restructured the test a bit, to be less sensitive to this. Instead 
> of sleeping and then checking if uncommit has happened, the test will 
> now wait until uncommit happens and record the time. When checking the 
> time it now uses TIMEOUT_FACTOR to control how strict the check should be.
> 
> To keep things simple, I've also broken out the part that tests with 
> uncommit disabled into a separate test.
> 
> The change in ZPage/ZPageCache rounds up the last_used/last_committed 
> timestamps to the nearest second. Without this we will always be 
> rounding the time down, which means we can sometimes uncommit one second 
> too early, which is wrong but not a big problem, but this can also cause 
> TestUncommit.java to fail with "Uncommitted too fast".
> 
> Bug: https://bugs.openjdk.java.net/browse/JDK-8248266
> Webrev: http://cr.openjdk.java.net/~pliden/8248266/webrev.0
> 
> Testing: Ran TestUncommit 100+ times on all Oracle-platforms.
> 
> /Per