Add read_events and write_events to Array

[alexfikl]

Takes care of the first point from #303.

• Adds a read_events and write_events to Array.
• Teaches all the functions in cl.array to use those and not wait on read events when they don't need to.
• Teaches all the functions in cl.clmath to play nice as well
• The rest of the code just does a straight port form events -> write_events. This still needs work.

TODO:

• Needs corresponding loopy change

[alexfikl]

@inducer This should be in a non-horrible state now. Can you take a quick look to see if it's doing what you had in mind?

From going through it, it seems like several things still need work

• elwise_kernel_runner could probably add to write_events for the first arg and to read_events for the rest of them, so we don't clutter all the rest of the code. Does that sound reasonable?
• It seems to me that something like an C = AXPBY would need wait for read_events on C and write_events on A and B. Does that sound right? (+ similar logic for the other elementwise kernels)

[inducer]

• elwise_kernel_runner could probably add to write_events for the first arg and to read_events for the rest of them, so we don't clutter all the rest of the code. Does that sound reasonable?

Does.

• It seems to me that something like an C = AXPBY would need wait for read_events on C and write_events on A and B. Does that sound right? (+ similar logic for the other elementwise kernels)

The way I see it, it wouldn't have to wait on read_events, because read-after-read does not need synchronization. Or am I missing something?

[alexfikl]

The way I see it, it wouldn't have to wait on read_events, because read-after-read does not need synchronization. Or am I missing something?

In that example, C would be a write-after-read, right? That's why I was thinking that all the reads should finish before it gets modified.

[inducer]

• It seems to me that something like an C = AXPBY would need wait for read_events on C and write_events on A and B. Does that sound right? (+ similar logic for the other elementwise kernels)

C would need to wait for read_events and write_events, unless you'd make the two subsets of each other.

[alexfikl]

@inducer This should be ready for a look. It could probably use some more tests, but I'm not quite sure what we can do there. Any ideas?

[alexfikl]

@inducer This is the macos error I was worried about
https://github.com/inducer/pyopencl/actions/runs/3210604562/jobs/5248179538
but it seems to be happening on other branches as well, e.g.
https://github.com/inducer/pyopencl/actions/runs/3254926391/jobs/5343705664
so it's likely no biggie (?). With that in mind, I feel better about this not introducing any cool new bugs :D