RFR(XL): 8185640: Thread-local handshakes

Erik Österlund erik.osterlund at oracle.com
Fri Oct 27 08:36:42 UTC 2017

Hi Andrew,

On 2017-10-27 10:26, Andrew Haley wrote:
> On 27/10/17 08:11, Erik Österlund wrote:
>> The current mechanism does not use mprotect to stop threads.
> Eh?  Sure it does: you're talking about the new, proposed mechanism
> that's the subject of this patch, surely.

Yes indeed. Sorry, I was unclear.

>> It has one global trapping page and one global not trapping page. It
>> simply performs stores to flip the polling word to point at the
>> trapping page.  So I am not so concerned about TLB shootdown costs
>> here.  As for the SEGV, the mechanism was stress tested (shooting
>> handshakes on all threads continuously) to see how expensive the
>> SEGV was, and the outcome was that it was surprisingly cheap. So we
>> did not pursue making the slow path faster.
> Interesting.  It's a lot of code.



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