Struct SingleGpuBackend 

pub struct SingleGpuBackend;

Single-GPU backend: all collective ops are no-ops.

Used in Phase 1 where the entire model fits on one GPU.

Trait Implementations

impl CommBackend for SingleGpuBackend

fn all_reduce(&self, _ptr: u64, _bytes: usize) -> Result<()>

All-reduce: sum across all ranks, result on all ranks.

fn all_gather( &self, _send_ptr: u64, _recv_ptr: u64, _bytes: usize, ) -> Result<()>

All-gather: each rank contributes a chunk, all ranks get full buffer.

fn reduce_scatter( &self, _send_ptr: u64, _recv_ptr: u64, _bytes: usize, ) -> Result<()>

Reduce-scatter: reduce + scatter (inverse of all-gather).

fn broadcast(&self, _ptr: u64, _bytes: usize, _root: usize) -> Result<()>

Broadcast from root rank to all ranks.

fn barrier(&self) -> Result<()>

Barrier: block until all ranks reach this point.

fn send_to( &self, _ptr: u64, _bytes: usize, _dest_rank: usize, _stream: u64, ) -> Result<()>

Send tokens to a specific rank (for EP token dispatch).

fn recv_from( &self, _ptr: u64, _bytes: usize, _src_rank: usize, _stream: u64, ) -> Result<()>

Receive tokens from a specific rank (for EP token combine).

fn rank(&self) -> usize

This rank’s index (0-based).

fn world_size(&self) -> usize

Total number of ranks.

fn all_reduce_async( &self, ptr: u64, bytes: usize, compute_stream: u64, ) -> Result<()>

Async all-reduce using GPU-side event synchronization.

fn register_buffer(&self, _ptr: u64, _bytes: usize) -> Result<u64>

Pre-register a GPU buffer with the communication backend.

fn deregister_buffer(&self, _handle: u64) -> Result<()>

Deregister a previously registered buffer.

fn symmetric_alloc(&self, _bytes: usize) -> Result<u64>

Allocate a GPU buffer in NCCL’s symmetric-memory window (NCCL ≥ 2.28 / ncclMemAlloc). Returns the device pointer as u64.

fn symmetric_free(&self, _ptr: u64) -> Result<()>

Free a buffer previously returned by symmetric_alloc.

fn set_add_kernel(&self, _handle: u64)

Provide a kernel handle for the BF16 in-place addition kernel.

fn group_start(&self) -> Result<()>

Begin a group of point-to-point operations (send_to/recv_from).

fn group_end(&self) -> Result<()>

End a group of point-to-point operations.

fn is_healthy(&self) -> bool

Check if the communicator is healthy (no async errors, no timeouts).

fn attempt_reconnect(&self) -> Result<()>

Attempt to recover a degraded communicator.