context : restore preemptive sched reset when LLAMA_SET_ROWS=0 (#14870)

ggml-ci

src/llama-context.cpp

@@ -105,7 +105,7 @@ llama_context::llama_context(
 
     {
         const char * LLAMA_SET_ROWS = getenv("LLAMA_SET_ROWS");
-        const bool supports_set_rows = LLAMA_SET_ROWS ? (atoi(LLAMA_SET_ROWS) != 0) : false;
+        supports_set_rows = LLAMA_SET_ROWS ? (atoi(LLAMA_SET_ROWS) != 0) : false;
 
         if (!supports_set_rows && !cparams.kv_unified) {
             LLAMA_LOG_WARN("%s: non-unified KV cache requires ggml_set_rows() - forcing unified KV cache\n", __func__);
@@ -899,6 +899,12 @@ int llama_context::encode(const llama_batch & batch_inp) {
         }
     }
 
+    if (!supports_set_rows) {
+        // Reset state for the next token before backend sync, to allow the CPU activities in the reset to
+        // overlap with device computation.
+        ggml_backend_sched_reset(sched.get());
+    }
+
     // TODO: hacky solution
     if (model.arch == LLM_ARCH_T5 && t_embd) {
         //cross.t_embd = t_embd;
@@ -1229,6 +1235,12 @@ int llama_context::decode(const llama_batch & batch_inp) {
     // wait for the computation to finish (automatically done when obtaining the model output)
     //synchronize();
 
+    if (!supports_set_rows) {
+        // Reset state for the next token before backend sync, to allow the CPU activities in the reset to
+        // overlap with device computation.
+        ggml_backend_sched_reset(sched.get());
+    }
+
     return 0;
 }
 

src/llama-context.h

@@ -287,6 +287,10 @@ private:
 
     bool has_evaluated_once = false;
 
+    // env: LLAMA_SET_ROWS (temporary)
+    // ref: https://github.com/ggml-org/llama.cpp/pull/14285
+    bool supports_set_rows = false;
+
     // perf
     mutable int64_t t_start_us  = 0;
     mutable int64_t t_load_us   = 0;