Use the build environment as sccache prefix instead of workflow name (p…

…ytorch#144112)

This is an attempt to improve cache usage for jobs in non-pull workflows like periodic, slow, or inductor as we are seeing build timeout there from time to time, for example https://github.com/pytorch/pytorch/actions/runs/12553928804.  The build timeout never happens in pull or trunk AFAICT because they are more up to date with the cache content coming from the PR itself.

Logically, the same build should use the same cache regardless of the workflows.  We have many examples where the same build, for example [linux-focal-cuda12.4-py3.10-gcc9-sm86](https://github.com/search?q=repo%3Apytorch%2Fpytorch+linux-focal-cuda12.4-py3.10-gcc9-sm86&type=code), is split between different workflows and, thus, uses different caches.

I could gather some sccache stats from CH in the meantime to try to prove the improvement before and after this lands.
Pull Request resolved: pytorch#144112
Approved by: https://github.com/malfet

.github/workflows/_linux-build.yml

@@ -199,7 +199,10 @@ jobs:
           SHA1: ${{ github.event.pull_request.head.sha || github.sha }}
           SCCACHE_BUCKET: ossci-compiler-cache-circleci-v2
           SCCACHE_REGION: us-east-1
-          SCCACHE_S3_KEY_PREFIX: ${{ github.workflow }}
+          # Use the build environment here to make sure that all build jobs in the same environment
+          # will share the same cache regardless of which workflow they belong. This should improve
+          # the cache usage for jobs in non-pull workflows like periodic, slow, or inductor
+          SCCACHE_S3_KEY_PREFIX: ${{ inputs.build-environment || github.workflow }}
           XLA_CLANG_CACHE_S3_BUCKET_NAME: ossci-compiler-clang-cache-circleci-xla
           PR_LABELS: ${{ toJson(github.event.pull_request.labels.*.name) }}
           TORCH_CUDA_ARCH_LIST: ${{ inputs.cuda-arch-list }}

.github/workflows/_linux-test.yml

@@ -230,7 +230,10 @@ jobs:
           TD_DISTRIBUTED: ${{ steps.keep-going.outputs.ci-td-distributed }}
           SCCACHE_BUCKET: ossci-compiler-cache-circleci-v2
           SCCACHE_REGION: us-east-1
-          SCCACHE_S3_KEY_PREFIX: ${{ github.workflow }}
+          # Use the build environment here to make sure that all build jobs in the same environment
+          # will share the same cache regardless of which workflow they belong. This should improve
+          # the cache usage for jobs in non-pull workflows like periodic, slow, or inductor
+          SCCACHE_S3_KEY_PREFIX: ${{ inputs.build-environment || github.workflow }}
           SHM_SIZE: ${{ contains(inputs.build-environment, 'cuda') && '2g' || '1g' }}
           DOCKER_IMAGE: ${{ inputs.docker-image }}
           XLA_CUDA: ${{ contains(inputs.build-environment, 'xla') && '0' || '' }}