Symbol M

The passage around this formula

The consequence that matters operationally is that $T_{\text{opt}}$ shrinks as M shrinks, and M shrinks sharply as accelerator count grows — so a checkpoint interval tuned for a 512-GPU job is not a conservative choice for a 16,000-GPU job, it is simply wrong, and it will keep being wrong in the same direction as the fleet grows further. The only way to hold $T_{\text{opt}}$ steady as M falls is to drive C down, which is why so much of the published checkpointing literature is really about reducing checkpoint cost rather than changing checkpoint frequency directly.

Read this part in the article →