Discussion: 8172978: Remove Interpreter TOS optimization

[Doerr, Martin]

Hi Aleksey,

of course, the peak performance is not really affected by this change.
Ideally, one should measure the startup performance. However, these measurements are highly unstable, so one would need to spend more effort and many runs.
That's why we use interpreter only tests. They are very stable and give us a hint about what's happening.

The assumption behind this proposal was that interpreter performance would not suffer much on modern hardware.
The -Xint benchmark is able to show that this is not true.

Best regards,
Martin


-----Original Message-----
From: Aleksey Shipilev [mailto:shade at redhat.com] 
Sent: Dienstag, 28. Februar 2017 16:14
To: Doerr, Martin <martin.doerr at sap.com>; Max Ockner <max.ockner at oracle.com>; hotspot-dev at openjdk.java.net
Subject: Re: Discussion: 8172978: Remove Interpreter TOS optimization

On 02/28/2017 04:00 PM, Doerr, Martin wrote:
> I've ran jvm98 with -Xint on several PPC64 machines and on a recent s390x
> machine.
> 
> Surprisingly, disabling of the Tos optimization does not hurt on older
> hardware (Power 5 and 6). Seems like some sub benchmarks don't suffer at all
> or even benefit. But it really hurts on recent Power 8.

I don't think it makes sense to run performance tests with -Xint alone. Of
course removing interpreter optimizations would affect interpreter performance.
The real question one should ask if turning off an interpreter optimization
affects peak performance and time-to-performance when compilers are enabled.

That's because in 2017 we should not expect that users who need performance
would run with interpreter only. And removing complexity from interpreter
without sacrificing the performance in tiered/compiled mode is certainly a plus
in my book.

Thanks,
-Aleksey