On Fri, 6 Nov 2020 02:00:07 GMT, David Holmes <dhol...@openjdk.org> wrote:
>> Changes from @fisk and @dcubed-ojdk to:
>>
>> - simplify ObjectMonitor list management
>> - get rid of Type-Stable Memory (TSM)
>>
>> This change has been tested with Mach5 Tier[1-3],4,5,6,7,8; no new
>> regressions.
>> Aurora Perf runs have also been done (DaCapo-h2, Quick Startup/Footprint,
>> SPECjbb2015-Tuned-G1, SPECjbb2015-Tuned-ParGC, Volano)
>> - a few minor regressions (<= -0.24%)
>> - Volano is 6.8% better
>>
>> Eric C. has also done promotion perf runs on these bits and says "the
>> results look fine".
>
> src/hotspot/share/runtime/objectMonitor.hpp line 145:
>
>> 143: // have busy multi-threaded access. _header and _object are set at
>> initial
>> 144: // inflation. The _object does not change, so it is a good choice to
>> share
>> 145: // its the cache line with _header.
>
> Typo: its the
Nice catch. Fixed.
> src/hotspot/share/runtime/synchronizer.cpp line 60:
>
>> 58:
>> 59: void MonitorList::add(ObjectMonitor* m) {
>> 60: for (;;) {
>
> Style nit: a do/while loop would like nicer here.
Fixed:
do {
ObjectMonitor* head = Atomic::load(&_head);
m->set_next_om(head);
} while (Atomic::cmpxchg(&_head, head, m) != head);
> src/hotspot/share/runtime/synchronizer.cpp line 94:
>
>> 92: // Find next live ObjectMonitor.
>> 93: ObjectMonitor* next = m;
>> 94: while (next != NULL && next->is_being_async_deflated()) {
>
> Nit: This loop seems odd. Given we know m is_being_async_deflated, this
> should either be a do/while loop, or else we should initialize:
>
> ObjectMonitor* next = m->next_om();
>
> and dispense with the awkwardly named next_next.
@fisk - I'm leaving this one for you for now.
> src/hotspot/share/runtime/synchronizer.cpp line 126:
>
>> 124: }
>> 125:
>> 126: if (self->is_Java_thread() &&
>
> Non-JavaThreads may have a monitor list ???
This function, MonitorList::unlink_deflated(), may be called by
either the MonitorDeflationThread or the VMThread. The VMThread
does not need to block for the safepoint which is what the
`if (self->is_Java_thread()` prevents.
-------------
PR: https://git.openjdk.java.net/jdk/pull/642
