hparams : support models for which all layers use SWA (#13682)

ggml-ci

src/llama-hparams.cpp

@@ -72,7 +72,7 @@ uint32_t llama_hparams::n_embd_v_s() const {
 
 bool llama_hparams::is_swa(uint32_t il) const {
     if (il < n_layer) {
-        return n_swa > 0 && n_swa_pattern > 0 && il % n_swa_pattern < (n_swa_pattern - 1);
+        return n_swa_pattern == 0 || (il % n_swa_pattern < (n_swa_pattern - 1));
     }
 
     GGML_ABORT("fatal error");

src/llama-hparams.h

@@ -104,7 +104,18 @@ struct llama_hparams {
     llama_swa_type swa_type = LLAMA_SWA_TYPE_NONE;
 
     uint32_t n_swa = 0;         // the size of the sliding window (0 - no SWA)
-    uint32_t n_swa_pattern = 1; // by default, all layers use non-sliding-window attention
+    uint32_t n_swa_pattern = 1; // this value n means that every nth layer is dense (i.e. non-SWA)
+                                // by default n == 1, all layers are dense
+                                // note that if n_swa_pattern == 0, all layers are SWA
+                                // example: n_swa_pattern = 3
+                                //   il == 0: swa
+                                //   il == 1: swa
+                                //   il == 2: dense
+                                //   il == 3: swa
+                                //   il == 4: swa
+                                //   il == 5: dense
+                                //   il == 6: swa
+                                //   etc ...
 
     // for State Space Models
     uint32_t ssm_d_conv  = 0;