Hi Peter, Peter Levart <peter.lev...@gmail.com> wrote on 2017/09/18 22:05:43:
> From: Peter Levart <peter.lev...@gmail.com> > To: Kazunori Ogata <oga...@jp.ibm.com> > Cc: Hans Boehm <hbo...@google.com>, core-libs-dev <core-libs-dev@openjdk.java.net> > Date: 2017/09/18 22:06 > Subject: Re: RFR: 8187033: [PPC] Imporve performance of > ObjectStreamClass.getClassDataLayout() > > Hi Ogata, > > On 09/18/2017 12:28 PM, Kazunori Ogata wrote: > > Hi Hans and Peter, > > > > Thank you for your comments. > > > > Regarding the code Hans showed, I don't yet understand what it the > > problem. Since the load at 1204b is a speculative one, dereferencing > > slots[17] should not raise any exception. If the confirmation at 1204.5 > > succeeds, the value of tmp must also be correct because we put full fence > > and we see a non-NULL reference that was stored after the full fence. > > I don't know much, but I can imagine that speculative read may see the > value and guess it correctly based on let's say some CPU state of > half-processed write instruction in the pipeline, which is established > even before the fence instruction flushes writes to array slots. So I > can accept that such outcome is possible and doesn't violate JMM. This seems to me that the processor/platform can't implement full fence correctly. I think it is the platform's (processor's and compiler's) responsibility to support full fence, otherwise the platform can't implement all Java API, including VarHandle.fullFence(). <snip> > > @Peter, > > > > Thank you for the fix. I'll measure the performance. > > ClassDataLayout object (instead of ClassDataSlot[] array) is also an > opportunity to put into it some pre-computed cached state which is > re-computed frequently in ObjectInputStream.readSerialData and maybe > also ObjectOutputStream.writeSerialData. > > I'll show the variant which pre-computes the 'hasSpecialReadMethod' > value which is always recomputed in ObjectInputStream.readSerialData if > your benchmark shows this is a promising direction... Do you mean caching the result of ObjectStreamClass.hasReadObjectMethod()? If so, can we cache it, though ObjectStreamClass.readObjectMethod is a mutable field? Regards, Ogata P.S. I'm waiting for finishing a long-running job on my machine. I'll measure your patch tomorrow.
