## Building a pipeline

### Building Block
It starts by laying out the passes for a single microbatch, which we call a building
block. For example, the building block of 1F1B schedule is made of a sequence of forward passes
followed by backward passes in the reverse order.

### Repeating
More microbatches are then introduced. The building blocks are repeated and woven
together to form a pipeline. Notably, legit building blocks are required to repeat without a collision, namely, the
passes from two building blocks should not overlap with each other.

### Squeezing
Depending on the building block, there may be redundant bubbles in the pipeline, which
can be simply removed by squeezing without changing the order of the passes.

### Reordering (optional)
We can reorder the passes in the warm-up and cool-down phase to further
improve the computation throughput. Intuitively, the peak of memory happens in the stable phase of
the pipeline, while in the warm-up and cool-down phases the RAM is under utilized, leaving some
space for improving the computation throughput without changing peak memory.

## Alternative schedules

By utilizing the building block, we can search for different types of schedules depending on the need. We illustrate few of them here below:

* 1F1B-V schedule without doing any B-W split.
* Schedule with 2/3rd 1F1B memory by utilising B-W split. Note that two microbatches are included in a single building block to avoid collision.
* Variation of interleaved 1F1B with lower memory