RFR: JDK-8086056: ParNew: auto-tune ParGCCardsPerStrideChunk

[sangheon.kim]

Hi Tony,

On 07/02/2015 12:27 PM, Tony Printezis wrote:
> Sangheon,
>
> Thanks, well spotted. I did what Thomas suggested: allow the diff to 
> be 0 and make sure r is 0.0 when that happens.
Okay.

>
> FYA: I tried to cause the issue by setting min_capacity == 
> max_capacity and I couldn’t. Note the start of that method: the 
> calculation only takes place when min_capacity <= capacity <= 
> max_capacity. So, if min_capacity == max_capacity, both have to be == 
> capacity for the calculation to happen which will cause the div-by-0. :-)
Oh, I see.
Thanks for the result!

Sangheon


>
> Anyway, thanks again for bringing this up,
>
> Tony
>
> On July 1, 2015 at 8:03:32 PM, sangheon.kim (sangheon.kim at oracle.com 
> <mailto:sangheon.kim at oracle.com>) wrote:
>
>> Hi Tony,
>>
>> I just looked the calculation routine and if we set 
>> 'DynamicParGCStridesMinOldGenCapacity = 
>> DynamicParGCStridesMaxOldGenCapacity', division by zero would happen.
>> So if I understand correctly, the constraint of 'max' should be 
>> always greater than 'min', isn't it?
>>
>> http://cr.openjdk.java.net/~tonyp/8086056/webrev.2/src/share/vm/gc/cms/parNewGeneration.cpp.frames.html
>>
>>  885   const size_t min_old_gen_capacity = 
>> DynamicParGCStridesMinOldGenCapacity;
>>  886   const size_t max_old_gen_capacity = 
>> DynamicParGCStridesMaxOldGenCapacity;
>>
>>  902     const size_t capacity_diff = max_old_gen_capacity - 
>> min_old_gen_capacity;
>>  903     const size_t capacity_offset = capacity - min_old_gen_capacity;
>>  904     const double r = (double) capacity_offset / (double) 
>> *capacity_diff**;*
>>
>> Thanks,
>> Sangheon
>>
>>
>> On 07/01/2015 03:05 PM, Tony Printezis wrote:
>>> Latest changes, as discussed with Bengt and Thomas,
>>>
>>> http://cr.openjdk.java.net/~tonyp/8086056/webrev.2/ 
>>> <http://cr.openjdk.java.net/%7Etonyp/8086056/webrev.2/>
>>>
>>> Tony
>>>
>>> On June 26, 2015 at 9:37:45 AM, Thomas Schatzl 
>>> (thomas.schatzl at oracle.com <mailto:thomas.schatzl at oracle.com>) wrote:
>>>
>>>> Hi Tony,
>>>>
>>>> On Fri, 2015-06-26 at 09:30 -0400, Tony Printezis wrote:
>>>>
>>>> [...]
>>>> > >
>>>> > >
>>>> > > The JEP says:
>>>> > >
>>>> > > "The range and constraints checks are done every time a flag
>>>> > > changes, as well as late in the JVM initialization routine 
>>>> (i.e., in
>>>> > > init_globals() after stubRoutines_init2()) at the time when all
>>>> > > flags have their final values set. We will continue to check the
>>>> > > manageable flags as long as the JVM runs."
>>>> > >
>>>> > > I haven't actively been using this myself, but I assume that the
>>>> > > constraints will be checked every time a managaeble flag is changed
>>>> > > and that the one trying to change it will get an error reported 
>>>> back
>>>> > > if they try to change it in an invalid way.
>>>> > >
>>>> > > I'm copying Gerard on this email. He has built this support and can
>>>> > > surely answer the details.
>>>> >
>>>> > Hi, thanks. I’ll definitely look at it and change the code
>>>> > appropriately. BTW, has the change been integrated into the hs gc 
>>>> repo
>>>> > yet? (I don’t see it so I assume it hasn't.)
>>>>
>>>> You overlooked that a week or two ago we started to try out merging the
>>>> hs-rt and hs-gc repos to test whether doing so is beneficial in 
>>>> terms of
>>>> maintenance etc.
>>>>
>>>> So the hs-gc repo is currently discontinued. Please rebase your changes
>>>> to hs-rt. :)
>>>>
>>>> [...]
>>>> > >
>>>> > > Finally, just a heads up. I will be on vacation for the coming 
>>>> three
>>>> > > weeks. I doubt that I will be able to review any new version during
>>>> > > that time. If you get reviews from others I'm perfectly fine with
>>>> > > this being pushed. Depending on how different the changes that you
>>>> > > push are compared to the versions I've reviewed I'll leave it up to
>>>> > > you to decide whether you want to list me as a reviewer or not. I'm
>>>> > > fine either way. It's not a problem to leave me out of the reviewer
>>>> > > list if you are unsure.
>>>> >
>>>> > OK, thanks for letting me know! And enjoy your time off!!!!
>>>>
>>>> I will take over :)
>>>>
>>>> Thanks,
>>>> Thomas
>>>>
>>>>
>>>>
>>> -----
>>>
>>> Tony Printezis | JVM/GC Engineer / VM Team | Twitter
>>>
>>> @TonyPrintezis
>>> tprintezis at twitter.com <mailto:tprintezis at twitter.com>
>>>
>>
> -----
>
> Tony Printezis | JVM/GC Engineer / VM Team | Twitter
>
> @TonyPrintezis
> tprintezis at twitter.com <mailto:tprintezis at twitter.com>
>

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