RFR(XL): 8185640: Thread-local handshakes

[Robbin Ehn]

On 2017-10-27 15:21, Andrew Haley wrote:
> On 27/10/17 14:14, Robbin Ehn wrote:
>> We are discussing the opt-out option, the newest suggestion is to make it
>> diagnostic. Opinions?
> 
> We're working on ultra-low-pause-time garbage collection, and it would be very
> useful to be able to safepoint the interpreter at any bytecode, not at jumps.
> It is a performance-related option rather than diagonstic.
>

For that I suggest the e.g UseShenandoah to set a VM internal global setting to low latency.
Not exposing yet another option to the user.
And in dispatch_base look for that, e.g:

if (SafepointMechanism::uses_thread_local_poll() && table != safepoint_table &&
       (generate_poll || SOME_GLOBAL_SETTING_FOR_LOW_LATENCY)) {

When I get this into jdk10/hs, down-stream it to Shenandoah repo, do the benchmarks, upstream to jdk10/hs (ZGC might want this also).

/Robbin