llama : add custom RoPE (#2054)

* Implement customizable RoPE

The original RoPE has pre-defined parameters

theta_i = 10000^(−2(i−1)/d), for i in [1, 2, ..., d/2]

Our customizable RoPE, ggml_rope_custom_inplace, uses

theta_i = scale * base^(−2(i−1)/d), for i in [1, 2, ..., d/2]

with the default matches the original

scale = 1.0
base = 10000

The new command line arguments
--rope-freq-base
--rope-freq-scale
set the two new RoPE parameter.

Recent researches show changing these two parameters extends the context limit with minimal loss.

1. Extending Context to 8K
   kaiokendev
   https://kaiokendev.github.io/til#extending-context-to-8k

2. Extending Context Window of Large Language Models via Positional Interpolation
   Shouyuan Chen, Sherman Wong, Liangjian Chen, Yuandong Tian
   https://arxiv.org/abs/2306.15595

3. NTK-Aware Scaled RoPE allows LLaMA models to have extended (8k+) context size without any fine-tuning and minimal perplexity degradation.
   https://www.reddit.com/user/bloc97
   https://www.reddit.com/r/LocalLLaMA/comments/14lz7j5/ntkaware_scaled_rope_allows_llama_models_to_have/

For the bold, try adding the following command line parameters to your favorite model:
-c 16384 --rope-freq-base 80000 --rope-freq-scale 0.5

* ggml-metal: fix custom rope

* common: fix argument names in help

* llama: increase MEM_REQ_EVAL for MODEL_3B

It avoids crashing for quantized weights on CPU.
Better ways to calculate the required buffer size would be better.

* llama: make MEM_REQ_EVAL depend on n_ctx

* server: use proper Content-Type in curl examples

Without the header Content-Type: application/json, curl will POST with
Content-Type: application/x-www-form-urlencoded

Though our simple server doesn't care, the httplib.h used has a limit
with CPPHTTPLIB_FORM_URL_ENCODED_PAYLOAD_MAX_LENGTH 8192

With Content-Type: application/json, we can send large json data.

* style : minor fixes, mostly indentations

* ggml : fix asserts

---------

Co-authored-by: Georgi Gerganov <ggerganov@gmail.com>

examples/common.cpp

@@ -168,6 +168,18 @@ bool gpt_params_parse(int argc, char ** argv, gpt_params & params) {
                 break;
             }
             params.n_ctx = std::stoi(argv[i]);
+        } else if (arg == "--rope-freq-base") {
+            if (++i >= argc) {
+                invalid_param = true;
+                break;
+            }
+            params.rope_freq_base = std::stof(argv[i]);
+        } else if (arg == "--rope-freq-scale") {
+            if (++i >= argc) {
+                invalid_param = true;
+                break;
+            }
+            params.rope_freq_scale = std::stof(argv[i]);
         } else if (arg == "--memory-f32") {
             params.memory_f16 = false;
         } else if (arg == "--top-p") {
@@ -493,6 +505,8 @@ void gpt_print_usage(int /*argc*/, char ** argv, const gpt_params & params) {
     fprintf(stderr, "  --cfg-scale N         strength of guidance (default: %f, 1.0 = disable)\n", params.cfg_scale);
     fprintf(stderr, "  --cfg-smooth-factor N smooth factor between old and new logits (default: %f, 1.0 = no smoothing)\n", params.cfg_smooth_factor);
     fprintf(stderr, "  -c N, --ctx-size N    size of the prompt context (default: %d)\n", params.n_ctx);
+    fprintf(stderr, "  --rope-freq-base N    RoPE base frequency (default: %.1f)\n", params.rope_freq_base);
+    fprintf(stderr, "  --rope-freq-scale N   RoPE frequency scaling factor (default: %g)\n", params.rope_freq_scale);
     fprintf(stderr, "  --ignore-eos          ignore end of stream token and continue generating (implies --logit-bias 2-inf)\n");
     fprintf(stderr, "  --no-penalize-nl      do not penalize newline token\n");
     fprintf(stderr, "  --memory-f32          use f32 instead of f16 for memory key+value (default: disabled)\n");
@@ -573,6 +587,8 @@ struct llama_context_params llama_context_params_from_gpt_params(const gpt_param
     lparams.use_mlock    = params.use_mlock;
     lparams.logits_all   = params.perplexity;
     lparams.embedding    = params.embedding;
+    lparams.rope_freq_base  = params.rope_freq_base;
+    lparams.rope_freq_scale = params.rope_freq_scale;
 
     return lparams;
 }