RFR (XS): Enable UseCountedLoopSafepoints with Shenandoah

[Andrew Haley]

On 20/12/16 14:01, Roman Kennke wrote:
> Am Dienstag, den 20.12.2016, 13:32 +0000 schrieb Andrew Haley:
>> On 20/12/16 10:57, Aleksey Shipilev wrote:
>>> Since we care mostly about pause times, and not the raw throughput,
>>> it makes
>>> sense to enable safepoints in counted loops. This makes us much
>>> more responsive
>>> (as in, TTSP is lower) in many interesting scenarios.
>>
>> True, but I have seen some very interesting cases where we beat G1 in
>> throughput.
> 
> Yes. As far as I can see, those are not affected by this (e.g. compiler
> benchmarks). And multiple seconds (!) just to get to a safepoint seems
> way too much, and it's more than 1 program that is affected by this.

Can you tell me which program delays so long?  I'd like to see it.

I suspect that's a bug.  And, of course, people are capable of using
-XX:-UseCountedLoopSafepoints themselves.

>>   Let's not overdo this: at the very least we need to know
>> how to restore throughput when running Shenandoah;
> 
> easy: -XX:-UseCountedLoopSafepoints

Right, so we know for sure that enabling Shenandoah only affects one
other flag.  Good!

Andrew.