Reduce KV cache preallocation to 4096 and make it comptime configurable, add rm build note in readme, add note on comptime options in DEVELOPERS, make multiturn=0 the default

DEVELOPERS.md

@@ -70,3 +70,21 @@ The implementation code is roughly split into 4 layers, from high to low level:
 
 4.  Backend (`highway`) - Low-level hardware interface (SIMD in the case of
     highway) supporting the implementations in (3).
+
+## Compile-Time Flags (Advanced)
+
+There are several compile-time flags to be aware of (note these may or may not 
+be exposed to the build system):
+
+- `GEMMA_WEIGHT_T` : Sets the level of compression for weights (surfaced as 
+  WEIGHT_TYPE in CMakeLists.txt). Currently this should be set to `SfpStream` 
+  (default, if no flag is specified) for 8-bit SFP, or `hwy::bfloat16_t` to 
+  enable for higher-fidelity (but slower) bfloat16 support. This is defined in
+  `gemma.h`.
+- `GEMMA_MAX_SEQ_LEN` : Sets maximum sequence length to preallocate for the KV
+  Cache. The default is 4096 tokens but can be overridden. This is not exposed
+  through `CMakeLists.txt` yet. 
+
+In the medium term both of these will likely be deprecated in favor of handling
+options at runtime - allowing for multiple weight compression schemes in a single
+build and dynamically resizes the KV cache as needed.

README.md

@@ -114,8 +114,12 @@ convenient directory location (e.g. the `build/` directory in this repo).
 
 The build system uses [CMake](https://cmake.org/). To build the gemma inference
 runtime, create a build directory and generate the build files using `cmake`
-from the top-level project directory. For the 8-bit switched floating point
-weights (sfp), run cmake with no options:
+from the top-level project directory. Note if you previous ran `cmake` and are
+re-running with a different setting, be sure to clean out the `build/` directory
+with `rm -rf build/*` (warning this will delete any other files in the `build/` 
+directory.
+
+For the 8-bit switched floating point weights (sfp), run cmake with no options:
 
 #### Unix-like Platforms
 ```sh

configs.h

@@ -18,11 +18,16 @@
 #ifndef THIRD_PARTY_GEMMA_CPP_CONFIGS_H_
 #define THIRD_PARTY_GEMMA_CPP_CONFIGS_H_
 
+// Allow changing pre-allocated kv cache size as a compiler flag
+#ifndef GEMMA_MAX_SEQLEN
+#define GEMMA_MAX_SEQLEN 4096
+#endif // !GEMMA_MAX_SEQLEN
+
 #include <stddef.h>
 
 namespace gcpp {
 
-static constexpr size_t kSeqLen = 7168;
+static constexpr size_t kSeqLen = GEMMA_MAX_SEQLEN;
 
 struct ConfigGemma7B {
   static constexpr int kSeqLen = gcpp::kSeqLen;
@@ -31,7 +36,7 @@ struct ConfigGemma7B {
   static constexpr int kModelDim = 3072;
   static constexpr int kFFHiddenDim = 16 * 3072 / 2; // = 24576
   static constexpr int kHeads = 16;
-  static constexpr int kKVHeads = 16;  // standard MHA, no GQA or MQA
+  static constexpr int kKVHeads = 16; // standard MHA
   static constexpr int kQKVDim = 256; // query size == key size == value size
   static constexpr int kTopK = 1;
 };

gemma.h

@@ -29,10 +29,10 @@
 // copybara:import_next_line:gemma_cpp
 #include "configs.h" // kSeqLen
 // copybara:import_next_line:gemma_cpp
-#include "util/args.h"             // ArgsBase
 #include "hwy/aligned_allocator.h"
 #include "hwy/base.h" // hwy::bfloat16_t
 #include "hwy/contrib/thread_pool/thread_pool.h"
+#include "util/args.h" // ArgsBase
 // copybara:import_next_line:sentencepiece
 #include "src/sentencepiece_processor.h"
 
@@ -115,8 +115,7 @@ struct LoaderArgs : public ArgsBase<LoaderArgs> {
   Path cache; // compressed weights
   std::string model_type;
 
-  template <class Visitor>
-  void ForEach(const Visitor& visitor) {
+  template <class Visitor> void ForEach(const Visitor &visitor) {
     visitor(tokenizer, "tokenizer", Path(),
             "Path name of tokenizer model file. (required)");
     visitor(
@@ -176,8 +175,7 @@ struct InferenceArgs : public ArgsBase<InferenceArgs> {
     return nullptr;
   }
 
-  template <class Visitor>
-  void ForEach(const Visitor& visitor) {
+  template <class Visitor> void ForEach(const Visitor &visitor) {
     visitor(max_tokens, "max_tokens", size_t{3072},
             "Maximum number of tokens in prompt + generation.");
     visitor(max_generated_tokens, "max_generated_tokens", size_t{2048},
@@ -186,10 +184,9 @@ struct InferenceArgs : public ArgsBase<InferenceArgs> {
     visitor(temperature, "temperature", 1.0f, "Temperature for top-K", 2);
     visitor(deterministic, "deterministic", false,
             "Make top-k sampling deterministic", 2);
-    visitor(multiturn, "multiturn", true,
+    visitor(multiturn, "multiturn", false,
             "Multiturn mode (if 0, this clears the KV cache after every "
-            "interaction without quitting)",
-            2);
+            "interaction without quitting)\n    Default = 0 (conversation resets every turn)");
   }
 };