RFR(L): 8235795: replace monitor list mux{Acquire,Release}(&gListLock) with spin locks

[Daniel D. Daugherty]

Greetings,

I'm looking for a second reviewer on this thread. I've gone ahead and
made changes based on David H's comments on CR0.

     JDK-8235795 replace monitor list mux{Acquire,Release}(&gListLock) 
with spin locks
     https://bugs.openjdk.java.net/browse/JDK-8235795

Copyright years will be updated when the patches are rebased to JDK15.

Here's the incremental webrev URL:

http://cr.openjdk.java.net/~dcubed/8235795-webrev/1-for-jdk15.inc/

Here's the full webrev URL:

http://cr.openjdk.java.net/~dcubed/8235795-webrev/1-for-jdk15.full/

Here's what changed between CR0 and CR1:

   - refactor common code
   - refactor atomic load of LVars.population in 
monitors_used_above_threshold
   - simplify list walking in ObjectSynchronizer::om_release() so we 
lock fewer ObjectMonitors
   - remove unnecessary locking from 
ObjectSynchronizer::deflate_monitor_list()
   - add NoSafepointVerifier helpers to main list management functions
   - remove unnecessary storestore()
   - remove unnecessary comments
   - clarify/fix comments.

These changes have been tested in a Mach5 Tier[1-3] run with no
regressions. They have also been merged with 8235931 and 8236035 and
included in a Mach5 Tier[1-8] run with no known regressions (so far
since Tier8 is not quite finished).

I did a SPECjbb2015 run on these bits with a jdk-14+32 baseline and 25 runs:

     criticalJOPS                 0.25%  (Non-significant)
                    66754.32   66923.08
                   ± 1209.80  ± 1585.09
                              p = 0.674

     maxJOPS                     -1.12%  (Non-significant)
                    90965.80   89948.80
                   ± 1788.39  ± 1989.22
                              p = 0.063

I did a SPECjbb2015 run on the merge of 8235931, 8236035, and 8235795
with a jdk-14+32 baseline and 25 runs:

     criticalJOPS                 0.37%  (Non-significant)
                    66754.32   67003.92
                   ± 1209.80  ± 1662.01
                              p = 0.547

     maxJOPS                     -0.23%  (Non-significant)
                    90965.80   90754.00
                   ± 1788.39  ± 1851.64
                              p = 0.683

All of these results were flagged as "Non-significant" by the perf
testing system. Looks like "p" values are still too high.

Thanks, in advance, for comments, questions or suggestions.

Dan


On 12/23/19 4:57 PM, Daniel D. Daugherty wrote:
> Greetings,
>
> I'm extracting another standalone fix from the Async Monitor Deflation
> project (JDK-8153224) and sending it out for review (and testing)
> separately.
>
>     JDK-8235795 replace monitor list mux{Acquire,Release}(&gListLock) 
> with spin locks
>     https://bugs.openjdk.java.net/browse/JDK-8235795
>
> Here's the webrev URL:
>
> http://cr.openjdk.java.net/~dcubed/8235795-webrev/0-for-jdk15/
>
> Folks that have reviewed JDK-8153224 will recognize these changes as
> a subset of the monitor list changes from the Async Monitor Deflation
> project. It's a subset because the Async Monitor Deflation project
> needs additional spin locking due to the async deflation work.
>
> The OpenJDK wiki for Async Monitor Deflation has several sections
> dedicated to the Spin-Lock Monitor List Management changes. This
> link will get you to the first section:
>
> Spin-Lock Monitor List Management In Theory
> https://wiki.openjdk.java.net/display/HotSpot/Async+Monitor+Deflation#AsyncMonitorDeflation-Spin-LockMonitorListManagementInTheory 
>
>
> The remaining monitor list sections are:
>
> Background: ObjectMonitor Movement Between the Lists
> https://wiki.openjdk.java.net/display/HotSpot/Async+Monitor+Deflation#AsyncMonitorDeflation-Background:ObjectMonitorMovementBetweentheLists 
>
>
> Spin-Lock Monitor List Management In Reality
> https://wiki.openjdk.java.net/display/HotSpot/Async+Monitor+Deflation#AsyncMonitorDeflation-Spin-LockMonitorListManagementInReality 
>
>
> Using The New Spin-Lock Monitor List Functions
> https://wiki.openjdk.java.net/display/HotSpot/Async+Monitor+Deflation#AsyncMonitorDeflation-UsingTheNewSpin-LockMonitorListFunctions 
>
>
> Of course, the OpenJDK wiki content is specific to the Async Monitor
> Deflation project, but this extract is a very close subset.
>
> These changes have been tested in various Mach5 Tier[1-7] runs.
> I'm also doing SPECjbb2015 runs.
>
> Thanks, in advance, for comments, questions or suggestions.
>
> Dan
>