improve scratch buffer estimates

gpu/gpu.go

@@ -190,13 +190,7 @@ func getCPUMem() (memInfo, error) {
 func CheckVRAM() (int64, error) {
 	gpuInfo := GetGPUInfo()
 	if gpuInfo.FreeMemory > 0 && (gpuInfo.Library == "cuda" || gpuInfo.Library == "rocm") {
-		// leave 10% or 512MiB of VRAM free per GPU to handle unaccounted for overhead
+		return int64(gpuInfo.FreeMemory), nil
-		overhead := gpuInfo.FreeMemory / 10
-		gpus := uint64(gpuInfo.DeviceCount)
-		if overhead < gpus*512*1024*1024 {
-			overhead = gpus * 512 * 1024 * 1024
-		}
-		return int64(gpuInfo.FreeMemory - overhead), nil
 	}
 
 	return 0, fmt.Errorf("no GPU detected") // TODO - better handling of CPU based memory determiniation

llm/llm.go

@@ -50,10 +50,10 @@ func New(workDir, model string, adapters, projectors []string, opts api.Options)
 	// fp16 k,v matrices require = n_ctx * n_layer * n_embd / n_head * n_head_kv * 2 bytes each * 2 key and value
 	kv := 2 * 2 * int64(opts.NumCtx) * int64(ggml.NumLayers()) * int64(ggml.NumEmbed()) * int64(ggml.NumHeadKv()) / int64(ggml.NumHead())
 
-	// this amount is the overhead + tensors in memory
+	// rough estimation for scratch space based on context size, batch size and number of layers in the model
-	// TODO: get this from the llama.cpp's graph calculations instead of
+	// TODO: instead call llama.cpp's alloc functions to measure required memory
-	// estimating it's 1/6 * kv_cache_size * num_gqa
+	// TODO: account for quantization levels
-	graph := int64(ggml.NumGQA()) * kv / 6
+	scratch := 8*int64(opts.NumCtx)*int64(opts.NumBatch)*int64(ggml.NumLayers()) + 1536*1024*1024 // 1536MiB overhead
 
 	info := gpu.GetGPUInfo()
 	switch runtime.GOOS {
@@ -62,7 +62,7 @@ func New(workDir, model string, adapters, projectors []string, opts api.Options)
 			break
 		}
 
-		if size+kv+graph > vram {
+		if size+kv+scratch > vram {
 			slog.Info("not enough vram available, falling back to CPU only")
 			info.Library = "cpu"
 			info.Variant = gpu.GetCPUVariant()
@@ -99,13 +99,13 @@ func New(workDir, model string, adapters, projectors []string, opts api.Options)
 		maxlayers := int64(ggml.NumLayers()) + 1
 		devices := int64(info.DeviceCount)
 		avg := vram / devices
-		layers := maxlayers * (avg - graph) / (kv + size/devices)
+		layers := maxlayers * (avg - scratch) / (kv + size/devices)
 		if layers > maxlayers {
 			layers = maxlayers
 		}
 
 		// 1 + 2 must fit on the main gpu
-		min := graph + kv*layers/maxlayers
+		min := scratch + kv*layers/maxlayers
 		if layers <= 0 || min > avg {
 			slog.Info("not enough vram available, falling back to CPU only")
 			info.Library = "cpu"