[aarch64-port-dev ] RFR: 8243339: AArch64: Obsolete UseBarriersForVolatile option

[Andrew Haley]

On 5/14/20 11:39 AM, Andrew Dinn wrote:
> On 14/05/2020 11:15, Andrew Haley wrote:
>> On 5/14/20 11:07 AM, Xiaohong Gong wrote:
>>> Hi Andrew,
>>>
>>> Thanks for having a look at it!
>>>
>>>  > On 5/14/20 10:37 AM, Andrew Haley wrote:
>>>  > > On 5/14/20 9:48 AM, Andrew Dinn wrote:
>>>  > >> Just for references a direct link to the webrev, issue and CSR
>>>  > are:
>>>  > >>
>>>  > >>   https://cr.openjdk.java.net/~xgong/rfr/8243339/webrev.00/
>>>  > >>   https://bugs.openjdk.java.net/browse/JDK-8243339
>>>  > >>   https://bugs.openjdk.java.net/browse/JDK-8243456
>>>  > >>
>>>  > >> The webrev looks fine to me. Nice work, thank you!
>>>  > >
>>>  > > There's a problem with C1: we generate unnecessary DMBs if
>>>  > > we're using TieredStopAtLevel=1 or if we only have the client
>>>  > > compiler. This is a performance regression, so I reject this
>>>  > > patch.
>>>  >
>>>  > There are similar regressoins in the interpreter.
>>>
>>> Yes, I agree with you that regressions exist for interpreter and
>>> client compiler.  So do you think if it's better to add the
>>> conditions to add DMBs for C1 and interpreter?  How about just
>>> excluding the scenario like "interpreter only", "client compiler
>>> only" and "TieredStopAtLevel=1" ?
>>
>> Yes, I think so. Is there some way simply to ask the question "Are we
>> using C2 or JVMCI compilers?" That's what we need to know.
> This can be done using build time conditionality. 

Not entirely, because this is also switchable at runtime.

> Elsewhere in the code
> base we have:
> 
> #ifdef COMPILER2
>   . . .
> 
> #if INCLUDE_JVMCI
>   . . .
> 
> #if COMPILER2_OR_JVMCI
>   . . .
> 
> 
> regards,
> 
> 
> Andrew Dinn
> -----------
> 


-- 
Andrew Haley  (he/him)
Java Platform Lead Engineer
Red Hat UK Ltd. <https://www.redhat.com>
https://keybase.io/andrewhaley
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