Baffled asks: what does post_call_nop() do?

[Andrew Haley]

On 10/7/19 5:24 PM, Rickard Bäckman wrote:
> We use it to put metadata about the nmethod in there. Like offset to nmethod header for faster lookup. 

Aha! I would not have guessed.

> I’m wondering if those numbers are really attributed to the right instruction. 
> Change it to emit nothing and see if you get a 71% speedup. I’m
> guessing that % is really the call / return instruction and if
> post_call_nop wasn’t there it would just be added to the next
> instruction.

Mkay, thanks. I think you're right: the delay seems to be caused by a
horrendous pipeline stall in JMH's Blackhole::consume, nothing to do
with Loom.

-- 
Andrew Haley  (he/him)
Java Platform Lead Engineer
Red Hat UK Ltd. <https://www.redhat.com>
https://keybase.io/andrewhaley
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