cuda : fix vmm pool with multi GPU (#4620)

* cuda : fix vmm pool with multi GPU

* hip

* use recommended granularity instead of minimum

* better error checking

* fix mixtral

* use cudaMemcpy3DPeerAsync

* use cuda_pool_alloc in ggml_cuda_op_mul_mat

* consolidate error checking in ggml_cuda_set_device

* remove unnecessary inlines

ggml-ci

* style fixes

* only use vmm for the main device

* fix scratch buffer size, re-enable vmm pool for all devices

* remove unnecessary check id != g_main_device

1 files changed, 2 insertions, 1 deletions

diff --git a/llama.cpp b/llama.cpp
index 0b99f1e0..4aa59c4c 100644
--- a/llama.cpp
+++ b/llama.cpp
@@ -9519,7 +9519,8 @@ struct llama_context * llama_new_context_with_model(
             ctx->alloc = ggml_allocr_new_from_buffer(ctx->buf_alloc);
 #if defined(GGML_USE_CUBLAS) && !defined(LLAMA_GGML_BACKEND_CUDA_TEST)
             if (model->n_gpu_layers > 0) {
-                ggml_cuda_set_scratch_size(alloc_size);
+                // the CPU buffer adds this padding in case the malloc buffer is not aligned, so we need to do the same for the GPU buffer, since we use the same offsets
+                ggml_cuda_set_scratch_size(alloc_size + 64);
                 LLAMA_LOG_INFO("%s: VRAM scratch buffer: %.2f MiB\n", __func__, alloc_size / 1024.0 / 1024.0);
 
                 // calculate total VRAM usage