review (S) for 6978249: spill between cpu and fpu registers when those moves are fast

[Hiroshi Yamauchi]

Interesting. Thanks for the info.

On Fri, Aug 20, 2010 at 11:24 AM, Tom Rodriguez
<tom.rodriguez at oracle.com> wrote:
> It's very program and processor dependent.  If the moves are fast enough then it never appears to hurt and it can bring a small benefit for real programs.  Tight kernels with more live values can benefit more.  We're still getting a handle on the exact performance characteristics and hopefully will turn it on by default in some configs once we're more confident.  Anyway, your mileage may vary.
>
> tom
>
> On Aug 20, 2010, at 11:13 AM, Hiroshi Yamauchi wrote:
>
>> Hi Tom,
>>
>> I'm just curious - how much win is this spilling technique?
>>
>> Hiroshi
>>
>> On Thu, Aug 19, 2010 at 2:05 PM, Tom Rodriguez <tom.rodriguez at oracle.com> wrote:
>>>
>>> On Aug 19, 2010, at 1:49 PM, David Dabbs wrote:
>>>
>>>>
>>>> Tom Rodriguez wrote:
>>>>
>>>> --8< snip
>>>> [in addition to the register spilling changes]
>>>> I also moved the logic for PrintFlagsFinal since the initialization of
>>>> several subsystems may change some flag values which will be missed by
>>>> the current location.  Tested with scimark, ctw and the nsk tests on
>>>> 32 and 64 bit.
>>>>
>>>>
>>>> Does the "bundling" of the PrintFlagsFinal tweaks with the spilling mods
>>>> mean the former won't make it into JDK6 until HS19 lands there?
>>>
>>> Yes.  They could always be backported separately under a new bug id.  At the time it didn't seem worth a new bug id.
>>>
>>>>
>>>>
>>>> Thank you,
>>>>
>>>> David
>>>>
>>>>
>>>> p.s. Would this be the right list to post questions regarding HS flags
>>>> appropriate for
>>>> maximizing HotSpot performance on Nehalem CPUs?
>>>
>>> Yes it would be fine to ask about that here.  Mostly we autodetect and use the appropriate settings so there's not a lot which is or should be tuned.
>>>
>>> tom
>>>
>>>>
>>>>
>>>>
>>>>
>>>
>>>
>
>