RFR(XL): 8185640: Thread-local handshakes

Andrew Haley aph at redhat.com
Fri Oct 27 08:26:18 UTC 2017

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.

> 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.

Andrew Haley
Java Platform Lead Engineer
Red Hat UK Ltd. <https://www.redhat.com>
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