common: share thread pools when n_threads differ (#27138)

common/common.cpp

@@ -1750,6 +1750,18 @@ struct ggml_threadpool_params ggml_threadpool_params_from_cpu_params(const commo
     return tpp;
 }
 
+namespace {
+
+bool can_share_threadpool(const ggml_threadpool_params & tpp1, const ggml_threadpool_params & tpp2) {
+    // n_threads does not matter -> we'll use what's larger
+    ggml_threadpool_params tpp_comparison = tpp1;
+    tpp_comparison.n_threads = tpp2.n_threads;
+
+    return ggml_threadpool_params_match(&tpp_comparison, &tpp2);
+}
+
+}  // namespace
+
 common_threadpools::~common_threadpools() {
     if (!free_fn) {
         return;
@@ -1778,7 +1790,9 @@ void common_threadpools::init(llama_context * ctx, const common_params & params)
     struct ggml_threadpool_params tpp =
             ggml_threadpool_params_from_cpu_params(params.cpuparams);
 
-    if (!ggml_threadpool_params_match(&tpp, &tpp_batch)) {
+    if (can_share_threadpool(tpp, tpp_batch)) {
+        tpp.n_threads = std::max(tpp.n_threads, tpp_batch.n_threads);
+    } else {
         threadpool_batch = ggml_threadpool_new_fn(&tpp_batch);
         if (!threadpool_batch) {
             COM_WRN("batch threadpool create failed : n_threads %d\n", tpp_batch.n_threads);