bench: create fresh threadpool for each test

For benchmarking it's better to start a fresh pool for each test with the exact number of threads
needed for that test. Having larger pools is suboptimal (causes more load, etc).

examples/llama-bench/llama-bench.cpp

@@ -291,7 +291,6 @@ static void print_usage(int /* argc */, char ** argv) {
     printf("  -fa, --flash-attn <0|1>             (default: %s)\n", join(cmd_params_defaults.flash_attn, ",").c_str());
     printf("  -mmp, --mmap <0|1>                  (default: %s)\n", join(cmd_params_defaults.use_mmap, ",").c_str());
     printf("  --numa <distribute|isolate|numactl> (default: disabled)\n");
-    printf("  -mt, --max-threads <n>              (default: %d)\n", cmd_params_defaults.cpuparams.n_threads);
     printf("  -C, --cpu-mask <hex>                (default: 0x0)\n");
     printf("  --cpu-strict <0|1>                  (default: %d)\n", cmd_params_defaults.cpuparams.strict_cpu);
     printf("  --priority <0|1|2|3>                (default: %d)\n", cmd_params_defaults.cpuparams.priority);
@@ -499,12 +498,6 @@ static cmd_params parse_cmd_params(int argc, char ** argv) {
                 else if (value == "numactl")                    { params.numa = GGML_NUMA_STRATEGY_NUMACTL; }
                 else { invalid_param = true; break; }
             }
-        } else if (arg == "-mt" || arg == "--max-threads") {
-            if (++i >= argc) {
-                invalid_param = true;
-                break;
-            }
-            params.cpuparams.n_threads = std::stoi(argv[i]);
         } else if (arg == "-C" || arg == "--cpu-mask") {
             if (++i >= argc) {
                 invalid_param = true;
@@ -1435,21 +1428,6 @@ int main(int argc, char ** argv) {
 
     postprocess_cpu_params(params.cpuparams);
 
-    struct ggml_threadpool_params tpp;
-    tpp.n_threads      = params.cpuparams.n_threads;
-    tpp.mask_specified = params.cpuparams.mask_valid;
-    tpp.strict_cpu     = params.cpuparams.strict_cpu;
-    tpp.prio           = params.cpuparams.priority;
-    tpp.poll           = params.cpuparams.poll;
-
-    std::memcpy(&tpp.cpumask[0], &params.cpuparams.cpumask[0], GGML_MAX_N_THREADS);
-
-    struct ggml_compute_threadpool* threadpool = ggml_create_threadpool(&tpp);
-    if (!threadpool) {
-        LOG_TEE("%s: threadpool create failed : n_threads %d\n", __func__, tpp.n_threads);
-        exit(1);
-    }
-
     for (const auto & inst : params_instances) {
         // keep the same model between tests when possible
         if (!lmodel || !prev_inst || !inst.equal_mparams(*prev_inst)) {
@@ -1475,6 +1453,22 @@ int main(int argc, char ** argv) {
         test t(inst, lmodel, ctx);
 
         llama_kv_cache_clear(ctx);
+
+        struct ggml_threadpool_params tpp;
+        tpp.n_threads      = t.n_threads;
+        tpp.mask_specified = params.cpuparams.mask_valid;
+        tpp.strict_cpu     = params.cpuparams.strict_cpu;
+        tpp.prio           = params.cpuparams.priority;
+        tpp.poll           = params.cpuparams.poll;
+
+        std::memcpy(&tpp.cpumask[0], &params.cpuparams.cpumask[0], GGML_MAX_N_THREADS);
+
+        struct ggml_compute_threadpool* threadpool = ggml_create_threadpool(&tpp);
+        if (!threadpool) {
+            LOG_TEE("%s: threadpool create failed : n_threads %d\n", __func__, tpp.n_threads);
+            exit(1);
+        }
+
         llama_attach_threadpool(ctx, threadpool);
 
         // warmup run
@@ -1515,9 +1509,9 @@ int main(int argc, char ** argv) {
         llama_print_timings(ctx);
 
         llama_free(ctx);
-    }
 
-    ggml_release_threadpool(threadpool);
+        ggml_release_threadpool(threadpool);
+    }
 
     llama_free_model(lmodel);