RFR 8194085: Obsolete the deprecated SafepointSynchronize flags and remove related code

[harold seigel]

Thanks Coleen, Dan, and David for your comments!

Please review this updated webrev for bug JDK-8194085.

    http://cr.openjdk.java.net/~hseigel/bug_8194085.2/webrev/index.html

This updated webrev contains the changes suggested by Coleen, Dan, and 
David.

Thanks, Harold

On 2/22/2018 9:16 PM, David Holmes wrote:
> I should clarify expectation here. What I want to see is something 
> like this:
>
> 310           //    to drive subsequent spin/SwitchThreadTo()/Sleep(N) 
> decisions.
> 311
> 312           if (int(iterations) == -1) { // overflow - something is 
> wrong
> 313             guarantee (PageArmed == 0, "invariant") ; // 
> historical form
> 314           }
>
> I recommend keeping the same guarantee condition so that it can be 
> easily searched for in bug reports - even though it seems a little out 
> of place given we don't arm the page here.
>
> David
>
> On 23/02/2018 11:53 AM, David Holmes wrote:
>> On 23/02/2018 12:47 AM, Daniel D. Daugherty wrote:
>>> On 2/21/18 11:49 PM, David Holmes wrote:
>>>> Hi Harold,
>>>>
>>>> On 22/02/2018 4:31 AM, harold seigel wrote:
>>>>> Hi,
>>>>>
>>>>> Please review this JDK-11 change to obsolete the 
>>>>> SafepointSpinBeforeYield, DeferThrSuspendLoopCount, and 
>>>>> DeferPollingPageLoopCount options and related code.  With this 
>>>>> change, these options are still accepted on the command line but 
>>>>> have no affect other than to generate these warning messages:
>>>>>
>>>>>     Java HotSpot(TM) 64-Bit Server VM warning: Ignoring option
>>>>>     SafepointSpinBeforeYield; support was removed in 11.0
>>>>>     Java HotSpot(TM) 64-Bit Server VM warning: Ignoring option
>>>>>     DeferThrSuspendLoopCount; support was removed in 11.0
>>>>>     Java HotSpot(TM) 64-Bit Server VM warning: Ignoring option
>>>>>     DeferPollingPageLoopCount; support was removed in 11.0
>>>>
>>>> Just for the record these were once useful tuning values for 
>>>> investigating safepoint performance issues in the field.
>>>>
>>>>> Open Webrev: 
>>>>> http://cr.openjdk.java.net/~hseigel/bug_8194085/webrev/index.html
>>>>
>>>> This one is a bit messier than I had envisaged: -Xconcurrentio ?? 
>>>> Wow! :) Definitely overlooked that one. It should be deprecated in 
>>>> 11 for certain.
>>>>
>>>> I have one problem with a change in safepoint.cpp, the removal of 
>>>> this:
>>>>
>>>>  312           if (SafepointMechanism::uses_global_page_poll() && 
>>>> int(iterations) == DeferPollingPageLoopCount) {
>>>>  313             guarantee (PageArmed == 0, "invariant") ;
>>>>  314             PageArmed = 1 ;
>>>>  315             os::make_polling_page_unreadable();
>>>>  316           }
>>>>
>>>> This block triggers a guarantee failure if we fail to reach a 
>>>> safepoint and the number of iterations overflows to reach -1 (the 
>>>> value of DeferPollingPageLoopCount). That is the only thing that 
>>>> stops the VM from just hanging when we have an issue reaching 
>>>> safepoints (like all of the "counted loop" problems!) and is very 
>>>> valuable in clearly identifying the problem. So I strongly 
>>>> recommend that this is restored with an explicit check against -1.
>>>
>>> Hmmmm... I guess I'm not seeing why the changes here don't
>>> solve that problem:
>>>
>>>>   190     if (SafepointMechanism::uses_global_page_poll()) {
>>>>   191       // Make interpreter safepoint aware
>>>>   192       Interpreter::notice_safepoints();
>>>>   193
>>>> 194 if (DeferPollingPageLoopCount < 0) {
>>>>   195         // Make polling safepoint aware
>>>>   196         guarantee (PageArmed == 0, "invariant") ;
>>>>   197         PageArmed = 1 ;
>>>>   198         os::make_polling_page_unreadable();
>>>>   199       }
>>>> 200 }
>>>
>>> So L194 and L200 are deleted and the same block is always
>>> run when SafepointMechanism::uses_global_page_poll() is true
>>> and this happens before the "L221: while(still_running > 0) {"
>>>
>>> Did I miss something?
>>
>> That block is executed once.
>>
>> The deleted block is executed in the loop while trying to reach the 
>> safepoint and so detects excessive looping because we can't get to 
>> the safepoint.
>>
>> David
>>
>>> Dan
>>>
>>>
>>>>
>>>> ---
>>>>
>>>> src/hotspot/share/runtime/safepoint.hpp
>>>>
>>>> +   static void set_throughput_mode() {
>>>> +     _defer_thr_suspend_loop_count = 1;
>>>> +   }
>>>>
>>>> First can you add a comment before this that it is only used for 
>>>> -Xconcurrentio support.
>>>>
>>>> Second, the name seems odd - throughput mode? How about 
>>>> set_concurrentio_mode() ? Or even just 
>>>> set_defer_thr_suspend_loop_count() ?
>>>>
>>>> Thanks,
>>>> David
>>>> -----
>>>>
>>>>> JBS Bug: https://bugs.openjdk.java.net/browse/JDK-8194085
>>>>>
>>>>> The change was tested with Mach5 tiers 1 and 2 on all Mach5 
>>>>> platforms and tiers 3-5 in Linux-X64.
>>>>>
>>>>> Thanks, Harold
>>>