- "When you want to use a subset of the available GPUs, you can use",
- "the [TT]-gpu_id[tt] option, where GPU id's are passed as a string,",
- "e.g. 02 for using GPUs 0 and 2. When you want different GPU id's",
- "on different nodes of a compute cluster, use the GMX_GPU_ID environment",
- "variable instead. The format for GMX_GPU_ID is identical to ",
- "[TT]-gpu_id[tt], but an environment variable can have different values",
- "on different nodes of a cluster.",
+ "To use a subset of the available GPUs, or to manually provide a mapping of",
+ "GPUs to PP ranks, you can use the [TT]-gpu_id[tt] option. The argument of [TT]-gpu_id[tt] is",
+ "a string of digits (without delimiter) representing device id-s of the GPUs to be used.",
+ "For example, \"[TT]02[tt]\" specifies using GPUs 0 and 2 in the first and second PP ranks per compute node",
+ "respectively. To select different sets of GPU-s",
+ "on different nodes of a compute cluster, use the [TT]GMX_GPU_ID[tt] environment",
+ "variable instead. The format for [TT]GMX_GPU_ID[tt] is identical to ",
+ "[TT]-gpu_id[tt], with the difference that an environment variable can have",
+ "different values on different compute nodes. Multiple MPI ranks on each node",
+ "can share GPUs. This is accomplished by specifying the id(s) of the GPU(s)",
+ "multiple times, e.g. \"[TT]0011[tt]\" for four ranks sharing two GPUs in this node.",
+ "This works within a single simulation, or a multi-simulation, with any form of MPI.",