Multi GPU support, CUDA refactor, CUDA scratch buffer (#1703)

* CUDA multi GPU + scratch

ggml_cuda_compute_forward

Tensor parallelism

ggml_cuda_add

ggml_cuda_rms_norm

ggml_cuda_silu

CUDA scratch buffer

--main-gpu CLI option

5 files changed, 102 insertions, 7 deletions

diff --git a/examples/common.cpp b/examples/common.cpp
index b5810f2..c373462 100644
--- a/examples/common.cpp
+++ b/examples/common.cpp
@@ -9,6 +9,7 @@
 #include <algorithm>
 #include <sstream>
 #include <unordered_set>
+#include <regex>
 
 #if defined(__APPLE__) && defined(__MACH__)
 #include <sys/types.h>
@@ -295,6 +296,40 @@ bool gpt_params_parse(int argc, char ** argv, gpt_params & params) {
             fprintf(stderr, "warning: not compiled with GPU offload support, --n-gpu-layers option will be ignored\n");
             fprintf(stderr, "warning: see main README.md for information on enabling GPU BLAS support\n");
 #endif
+        } else if (arg == "--main-gpu" || arg == "-mg") {
+            if (++i >= argc) {
+                invalid_param = true;
+                break;
+            }
+#ifdef GGML_USE_CUBLAS
+            params.main_gpu = std::stoi(argv[i]);
+#else
+      fprintf(stderr, "warning: llama.cpp was compiled without cuBLAS. It is not possible to set a main GPU.\n");
+#endif
+        } else if (arg == "--tensor-split" || arg == "-ts") {
+            if (++i >= argc) {
+                invalid_param = true;
+                break;
+            }
+#ifdef GGML_USE_CUBLAS
+            std::string arg_next = argv[i];
+
+            // split string by , and /
+            const std::regex regex{R"([,/]+)"};
+            std::sregex_token_iterator it{arg_next.begin(), arg_next.end(), regex, -1};
+            std::vector<std::string> split_arg{it, {}};
+            GGML_ASSERT(split_arg.size() <= LLAMA_MAX_DEVICES);
+
+            for (size_t i = 0; i < LLAMA_MAX_DEVICES; ++i) {
+                if (i < split_arg.size()) {
+                    params.tensor_split[i] = std::stof(split_arg[i]);
+                } else {
+                    params.tensor_split[i] = 0.0f;
+                }
+            }
+#else
+      fprintf(stderr, "warning: llama.cpp was compiled without cuBLAS. It is not possible to set a tensor split.\n");
+#endif // GGML_USE_CUBLAS
         } else if (arg == "--no-mmap") {
             params.use_mmap = false;
         } else if (arg == "--mtest") {
@@ -438,6 +473,9 @@ void gpt_print_usage(int /*argc*/, char ** argv, const gpt_params & params) {
 #ifdef LLAMA_SUPPORTS_GPU_OFFLOAD
     fprintf(stderr, "  -ngl N, --n-gpu-layers N\n");
     fprintf(stderr, "                        number of layers to store in VRAM\n");
+    fprintf(stderr, "  -ts SPLIT --tensor-split SPLIT\n");
+    fprintf(stderr, "                        how to split tensors across multiple GPUs, comma-separated list of proportions, e.g. 3,1\n");
+    fprintf(stderr, "  -mg i, --main-gpu i   the GPU to use for scratch and small tensors\n" );
 #endif
     fprintf(stderr, "  --mtest               compute maximum memory usage\n");
     fprintf(stderr, "  --export              export the computation graph to 'llama.ggml'\n");
@@ -483,7 +521,10 @@ struct llama_context * llama_init_from_gpt_params(const gpt_params & params) {
     auto lparams = llama_context_default_params();
 
     lparams.n_ctx        = params.n_ctx;
+    lparams.n_batch      = params.n_batch;
     lparams.n_gpu_layers = params.n_gpu_layers;
+    lparams.main_gpu     = params.main_gpu;
+    memcpy(lparams.tensor_split, params.tensor_split, LLAMA_MAX_DEVICES*sizeof(float));
     lparams.seed         = params.seed;
     lparams.f16_kv       = params.memory_f16;
     lparams.use_mmap     = params.use_mmap;
diff --git a/examples/common.h b/examples/common.h
index 66bdeb5..12b4973 100644
--- a/examples/common.h
+++ b/examples/common.h
@@ -21,13 +21,15 @@
 int32_t get_num_physical_cores();
 
 struct gpt_params {
-    int32_t seed          = -1;  // RNG seed
-    int32_t n_threads     = get_num_physical_cores();
-    int32_t n_predict     = -1;  // new tokens to predict
-    int32_t n_ctx         = 512; // context size
-    int32_t n_batch       = 512; // batch size for prompt processing (must be >=32 to use BLAS)
-    int32_t n_keep        = 0;   // number of tokens to keep from initial prompt
-    int32_t n_gpu_layers  = 0;   // number of layers to store in VRAM
+    int32_t seed                           = -1;   // RNG seed
+    int32_t n_threads                      = get_num_physical_cores();
+    int32_t n_predict                      = -1;   // new tokens to predict
+    int32_t n_ctx                          = 512;  // context size
+    int32_t n_batch                        = 512;  // batch size for prompt processing (must be >=32 to use BLAS)
+    int32_t n_keep                         = 0;    // number of tokens to keep from initial prompt
+    int32_t n_gpu_layers                   = 0;    // number of layers to store in VRAM
+    int32_t main_gpu                       = 0;    // the GPU that is used for scratch and small tensors
+    float   tensor_split[LLAMA_MAX_DEVICES] = {0}; // how split tensors should be distributed across GPUs
 
     // sampling parameters
     std::unordered_map<llama_token, float> logit_bias; // logit bias for specific tokens
diff --git a/examples/main/README.md b/examples/main/README.md
index dd08749..149d507 100644
--- a/examples/main/README.md
+++ b/examples/main/README.md
@@ -286,5 +286,7 @@ These options provide extra functionality and customization when running the LLa
 -   `--verbose-prompt`: Print the prompt before generating text.
 -   `--mtest`: Test the model's functionality by running a series of tests to ensure it's working properly.
 -   `-ngl N, --n-gpu-layers N`: When compiled with appropriate support (currently CLBlast or cuBLAS), this option allows offloading some layers to the GPU for computation. Generally results in increased performance.
+-   `-mg i, --main-gpu i`: When using multiple GPUs this option controls which GPU is used for small tensors for which the overhead of splitting the computation across all GPUs is not worthwhile. The GPU in question will use slightly more VRAM to store a scratch buffer for temporary results. By default GPU 0 is used. Requires cuBLAS.
+-   `-ts SPLIT, --tensor-split SPLIT`: When using multiple GPUs this option controls how large tensors should be split across all GPUs. `SPLIT` is a comma-separated list of non-negative values that assigns the proportion of data that each GPU should get in order. For example, "3,2" will assign 60% of the data to GPU 0 and 40% to GPU 1. By default the data is split in proportion to VRAM but this may not be optimal for performance. Requires cuBLAS.
 -   `--lora FNAME`: Apply a LoRA (Low-Rank Adaptation) adapter to the model (implies --no-mmap). This allows you to adapt the pretrained model to specific tasks or domains.
 -   `--lora-base FNAME`: Optional model to use as a base for the layers modified by the LoRA adapter. This flag is used in conjunction with the `--lora` flag, and specifies the base model for the adaptation.
diff --git a/examples/server/README.md b/examples/server/README.md
index bba513c..b011302 100644
--- a/examples/server/README.md
+++ b/examples/server/README.md
@@ -287,6 +287,8 @@ Test();
 -   `-m FNAME, --model FNAME`: Specify the path to the LLaMA model file (e.g., `models/7B/ggml-model.bin`).
 -   `-c N, --ctx-size N`: Set the size of the prompt context. The default is 512, but LLaMA models were built with a context of 2048, which will provide better results for longer input/inference.
 -   `-ngl N, --n-gpu-layers N`: When compiled with appropriate support (currently CLBlast or cuBLAS), this option allows offloading some layers to the GPU for computation. Generally results in increased performance.
+-   `-mg i, --main-gpu i`: When using multiple GPUs this option controls which GPU is used for small tensors for which the overhead of splitting the computation across all GPUs is not worthwhile. The GPU in question will use slightly more VRAM to store a scratch buffer for temporary results. By default GPU 0 is used. Requires cuBLAS.
+-   `-ts SPLIT, --tensor-split SPLIT`: When using multiple GPUs this option controls how large tensors should be split across all GPUs. `SPLIT` is a comma-separated list of non-negative values that assigns the proportion of data that each GPU should get in order. For example, "3,2" will assign 60% of the data to GPU 0 and 40% to GPU 1. By default the data is split in proportion to VRAM but this may not be optimal for performance. Requires cuBLAS.
 -   `--embedding`: Enable the embedding mode. **Completion function doesn't work in this mode**.
 -   `--host`: Set the hostname or ip address to listen. Default `127.0.0.1`;
 -   `--port`: Set the port to listen. Default: `8080`.
diff --git a/examples/server/server.cpp b/examples/server/server.cpp
index 9aa7db2..31d8087 100644
--- a/examples/server/server.cpp
+++ b/examples/server/server.cpp
@@ -401,6 +401,10 @@ void server_print_usage(int /*argc*/, char **argv, const gpt_params &params)
 #ifdef LLAMA_SUPPORTS_GPU_OFFLOAD
   fprintf(stderr, "  -ngl N, --n-gpu-layers N\n");
   fprintf(stderr, "                        number of layers to store in VRAM\n");
+  fprintf(stderr, "  -ts SPLIT --tensor-split SPLIT\n");
+  fprintf(stderr, "                        how to split tensors across multiple GPUs, comma-separated list of proportions, e.g. 3,1\n");
+  fprintf(stderr, "                        how to split tensors across multiple GPUs, comma-separated list of proportions, e.g. 3,1\n");
+  fprintf(stderr, "  -mg i, --main-gpu i   the GPU to use for scratch and small tensors\n" );
 #endif
   fprintf(stderr, "  -m FNAME, --model FNAME\n");
   fprintf(stderr, "                        model path (default: %s)\n", params.model.c_str());
@@ -504,6 +508,50 @@ bool server_params_parse(int argc, char **argv, server_params &sparams, gpt_para
       fprintf(stderr, "warning: see main README.md for information on enabling GPU BLAS support\n");
 #endif
     }
+    else if (arg == "--tensor-split" || arg == "-ts")
+    {
+      if (++i >= argc)
+      {
+        invalid_param = true;
+        break;
+      }
+#ifdef GGML_USE_CUBLAS
+      std::string arg_next = argv[i];
+
+      // split string by , and /
+      const std::regex regex{R"([,/]+)"};
+      std::sregex_token_iterator it{arg_next.begin(), arg_next.end(), regex, -1};
+      std::vector<std::string> split_arg{it, {}};
+      GGML_ASSERT(split_arg.size() <= LLAMA_MAX_DEVICES);
+
+      for (size_t i = 0; i < LLAMA_MAX_DEVICES; ++i)
+      {
+        if (i < split_arg.size())
+        {
+          params.tensor_split[i] = std::stof(split_arg[i]);
+        }
+        else
+        {
+          params.tensor_split[i] = 0.0f;
+        }
+      }
+#else
+      fprintf(stderr, "WARNING: llama.cpp was compiled without cuBLAS. It is not possible to set a tensor split.\n");
+#endif // GGML_USE_CUBLAS
+    }
+    else if (arg == "--main-gpu" || arg == "-mg")
+    {
+      if (++i >= argc)
+      {
+        invalid_param = true;
+        break;
+      }
+#ifdef GGML_USE_CUBLAS
+      params.main_gpu = std::stoi(argv[i]);
+#else
+      fprintf(stderr, "warning: llama.cpp was compiled without cuBLAS. It is not possible to set a main GPU.\n");
+#endif
+    }
     else
     {
       fprintf(stderr, "error: unknown argument: %s\n", arg.c_str());