Set TPU VM the default option

[infwinston]

This PR changes the default for TPU from TPU node to TPU VM as the former is now being deprecated by GCP.
for example, the tpu-v4 arch doesn't support TPU node (ref)

For Cloud TPU v4, only the TPU VM architecture is supported, so all TPUs referenced in this document use the TPU VM architecture.

Tested (run the relevant ones):

• Disable tpu node for v4
• Smoke tests
• Docs
• Any manual or new tests for this PR (please specify below)
• All smoke tests: pytest tests/test_smoke.py
• Relevant individual smoke tests: pytest tests/test_smoke.py::test_fill_in_the_name
• Backward compatibility tests: bash tests/backward_comaptibility_tests.sh

[github-actions]

This PR is stale because it has been open 120 days with no activity. Remove stale label or comment or this will be closed in 10 days.

[Michaelvll]

@infwinston Any updates?

[Michaelvll]

We need someone to take over this PR to get it in. This is requested by our user.

[Michaelvll]

Tested(88562fe):

• on master: sky launch examples/tpu/tpu_app.yaml -c test-tpu-node; on this PR: sky exec test-tpu-node examples/tpu/tpu_app.yaml; sky launch examples/tpu/tpu_app.yaml -c test-tpu-node
• sky launch examples/tpu/tpuvm_mnist.yaml
• pytest tests/test_smoke.py --tpu

[concretevitamin]

Thanks @Michaelvll @infwinston. Quick question.

[concretevitamin]

QQ: why handle here vs. in

skypilot/sky/resources.py

Line 47 in 88562fe

_VERSION = 13

?

[Michaelvll]

Good catch! Moved it to resources instead. : )

[concretevitamin]

May want to update https://skypilot.readthedocs.io/en/latest/reference/yaml-spec.html and https://skypilot.readthedocs.io/en/latest/reference/tpu.html too.

[Michaelvll]

Thanks @concretevitamin for the review! Updated the docs. PTAL

[Michaelvll]

Tested:

• master branch: sky launch -c test-tpu-node test.yaml; this PR: sky exec test-tpu-node test-with-acc-args.yaml

resources: 
  accelerators: tpu-v2-8

run: |
  echo "Hello World"

• master branch: sky launch -c test-tpu-vm test.yaml; this PR: sky exec test-tpu-vm test-without-args.yaml