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

[harold seigel]

Thanks David!

I'll move the flags to the "obsolete flags" section before pushing the 
change.

Harold

On 2/26/2018 1:08 AM, David Holmes wrote:
> Hi Harold,
>
> On 24/02/2018 1:41 AM, harold seigel wrote:
>> 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.
>
> src/hotspot/share/runtime/arguments.cpp
>
> It seems that when we actually obsolete a flag we should move its 
> entry down into the "obsolete flags" section of the table. No need to 
> see updated webrev for that.
>
> Other updates are fine to me.
>
> Thanks,
> 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
>>>>>
>>