[10] RFR: 8179040: Avoid Ticks::now calls when EventClassLoad is not enabled

[Ioi Lam]

Hi Claes,

The changes look good. Reviewed.

Thanks

- Ioi


On 8/23/17 5:32 AM, Claes Redestad wrote:
> Hi,
>
> this patch was never pushed due to an unfortunate interaction around 
> cancelling
> of events. Markus Grönlund has helped resolve these, while maintaining 
> the
> speedup:
>
> http://cr.openjdk.java.net/~redestad/8179040/hotspot.02/
>
> Thanks!
>
> /Claes
>
> On 04/25/2017 03:21 PM, Claes Redestad wrote:
>> Hi,
>>
>> this patch removes calling Ticks::now when EventClassLoad isn't 
>> enabled, which
>> has an effect on class loading performance:
>>
>> http://cr.openjdk.java.net/~redestad/8179040/hotspot.01/
>>
>> When tracing isn't enabled trace/tracing.hpp has dummy 
>> implementations which
>> are easily optimized away by a compiler, which I've verified happens 
>> on linux
>> OpenJDK builds with tracing disabled.
>>
>> On builds with tracing enabled then the changes means the call to get 
>> the time
>> only happen if the event is enabled, which achieves the sought after 
>> startup
>> optimization.
>>
>> Thanks!
>>
>> /Claes
>