From dee2a846b82f15d27f84a48fa387cb53e0d99c25 Mon Sep 17 00:00:00 2001
From: Georgi Gerganov <ggerganov@gmail.com>
Date: Mon, 27 Jul 2026 14:54:46 +0300
Subject: [PATCH] ggml : adjust logic for offloading ops to weight's backend
 (#25832)

* ggml : adjust logic for offloading ops to weight's backend

* llama : dsv4 graph fixes
---
 ggml/src/ggml-backend.cpp | 43 +++++++++++++++++++++++----------------
 src/llama-context.cpp     |  5 +++--
 src/models/deepseek4.cpp  |  6 +++++-
 3 files changed, 34 insertions(+), 20 deletions(-)

diff --git a/ggml/src/ggml-backend.cpp b/ggml/src/ggml-backend.cpp
index 87615921c0..7f4e252dca 100644
--- a/ggml/src/ggml-backend.cpp
+++ b/ggml/src/ggml-backend.cpp
@@ -906,26 +906,35 @@ static int ggml_backend_sched_backend_id_from_cur(ggml_backend_sched_t sched, st
     }
 
     // operations with weights are preferably run on the same backend as the weights
-    for (int i = 0; i < GGML_MAX_SRC; i++) {
-        const struct ggml_tensor * src = tensor->src[i];
-        if (src == NULL) {
-            continue;
-        }
-        // skip ROPE since the rope freqs tensor is too small to choose a backend based on it
-        // not an ideal solution
-        if (tensor->op != GGML_OP_ROPE && src->buffer != NULL && src->buffer->usage == GGML_BACKEND_BUFFER_USAGE_WEIGHTS) {
-            int src_backend_id = ggml_backend_sched_backend_from_buffer(sched, src, tensor);
-            // check if a backend with higher prio wants to offload the op
-            if (sched->op_offload && src_backend_id == sched->n_backends - 1 && ggml_backend_buffer_is_host(src->buffer)) {
-                for (int b = 0; b < src_backend_id; b++) {
-                    if (ggml_backend_supports_op(sched->backends[b], tensor) && ggml_backend_offload_op(sched->backends[b], tensor)) {
-                        SET_CAUSE(tensor, "1.off");
-                        return b;
+    // TODO: there are exceptions (see below) - not an ideal solution
+    bool allow = true;
+
+    // skip ROPE since the rope freqs tensor is too small to choose a backend based on it
+    allow = allow && tensor->op != GGML_OP_ROPE;
+
+    // skip FLASH_ATTN_EXT since the sinks tensor is too small to choose a based based on it
+    allow = allow && tensor->op != GGML_OP_FLASH_ATTN_EXT;
+
+    if (allow) {
+        for (int i = 0; i < GGML_MAX_SRC; i++) {
+            const struct ggml_tensor * src = tensor->src[i];
+            if (src == NULL) {
+                continue;
+            }
+            if (src->buffer != NULL && src->buffer->usage == GGML_BACKEND_BUFFER_USAGE_WEIGHTS) {
+                int src_backend_id = ggml_backend_sched_backend_from_buffer(sched, src, tensor);
+                // check if a backend with higher prio wants to offload the op
+                if (sched->op_offload && src_backend_id == sched->n_backends - 1 && ggml_backend_buffer_is_host(src->buffer)) {
+                    for (int b = 0; b < src_backend_id; b++) {
+                        if (ggml_backend_supports_op(sched->backends[b], tensor) && ggml_backend_offload_op(sched->backends[b], tensor)) {
+                            SET_CAUSE(tensor, "1.off");
+                            return b;
+                        }
                     }
                 }
+                SET_CAUSE(tensor, "1.wgt%d", i);
+                return src_backend_id;
             }
-            SET_CAUSE(tensor, "1.wgt%d", i);
-            return src_backend_id;
         }
     }
 
diff --git a/src/llama-context.cpp b/src/llama-context.cpp
index c512477c0e..012894e13f 100644
--- a/src/llama-context.cpp
+++ b/src/llama-context.cpp
@@ -2473,11 +2473,12 @@ llm_graph_cb llama_context::graph_get_cb() const {
             ggml_set_name(cur, name);
         }
 
-        // norm may be automatically assigned to the backend of the previous layer, increasing data transfer between backends
+        // - norm may be automatically assigned to the backend of the previous layer, increasing data transfer between backends
+        // - force the last op of the layer on the specified backend to avoid running it on the backend of the next layer due to scheduling
         // FIXME: fix in ggml_backend_sched
         const bool full_offload = model.n_gpu_layers() > model.hparams.n_layer_all;
         if (ubatch.n_tokens < 32 || full_offload) {
-            if (il != -1 && strcmp(name, "norm") == 0) {
+            if (il != -1 && (strcmp(name, "norm") == 0 || strcmp(name, "l_last") == 0)) {
                 const auto & dev_layer = model.dev_layer(il);
                 for (const auto & backend : backends) {
                     if (ggml_backend_get_device(backend.get()) == dev_layer) {
diff --git a/src/models/deepseek4.cpp b/src/models/deepseek4.cpp
index 5ad6473ce2..2d41dace0b 100644
--- a/src/models/deepseek4.cpp
+++ b/src/models/deepseek4.cpp
@@ -1133,6 +1133,10 @@ llama_model_deepseek4::graph::graph(const llama_model & model, const llm_graph_p
                 &post, &comb, il);
         cb(cur, "hc_ffn_pre", il);
 
+        ggml_build_forward_expand(gf, residual);
+        ggml_build_forward_expand(gf, post);
+        ggml_build_forward_expand(gf, comb);
+
         cur = build_norm(cur, model.layers[il].ffn_norm, nullptr, LLM_NORM_RMS, il);
         cb(cur, "ffn_norm", il);
 
@@ -1175,7 +1179,7 @@ llama_model_deepseek4::graph::graph(const llama_model & model, const llm_graph_p
 
         inpL = build_hc_post(cur, residual, post, comb, il);
         inpL = build_cvec(inpL, il);
-        cb(inpL, "l_out", il);
+        cb(inpL, "l_last", il);
     }
 
     if (inp_out_ids) {