Is the set of proposed instructions sufficient?

[binji]

The current proposal doesn't have much more than what is currently in ES. Do we want other instructions?

[lars-t-hansen]

One operation that never made it into ES was an instruction to relax in a spinloop (ie, the PAUSE instruction in x86, IIRC). It was in the very earliest drafts of the spec but I think that, more than anything, it was considered very low-level for ES and something that would create controversy. (I experimented with a related idea, a micro-wait primitive with a back-off scheme, and I called that "pause" too, but it's not what I'm talking about here.)

I know that PAUSE is important for performance on x86. I don't know if ARM has anything similar in eg its event instructions (WFE). I don't know if it's a good idea to push this through for the MVP since we won't be able to remove it again if it turns out to be the wrong thing.

[jfbastien]

Worth forking as a separate question, and polling (ha!) at the upcoming meeting.

[binji]

There wasn't a poll about this in the CG meeting, but there seemed to be interest in exploring adding a yield operation (as opposed to pause). This would be defined in the spec as being a no-op, but would be a hint to implementations to yield execution to another thread.

[binji]

As for other operations, we discussed other atomic primitives, including:

• neg
• min/max
• signed/unsigned (this is in the notes, but I can't recall what this means...)
• nand

We decided (without polling) that these other operations could be handled later if there is interest.