Fix imatrix calculation for MLA models (#411)

Co-authored-by: Iwan Kawrakow <iwan.kawrakow@gmail.com>

Author: ikawrakow

examples/imatrix/imatrix.cpp

@@ -60,7 +60,7 @@ class IMatrixCollector {
     int                                    m_last_call = 0;
     int                                    m_last_layer = 9999;
     int                                    m_last_ffn = -1;
-    std::vector<float>                     m_src1_data;
+    std::vector<char>                      m_src1_data;
     std::vector<char>                      m_ids; // the expert ids from ggml_mul_mat_id
     std::vector<float>                     m_last_input;
     std::vector<float>                     m_ffn_input;
@@ -189,11 +189,12 @@ bool IMatrixCollector::collect_imatrix(struct ggml_tensor * t, bool ask, void *
     const bool is_host = ggml_backend_buffer_is_host(src1->buffer);
 
     if (!is_host) {
-        m_src1_data.resize(ggml_nelements(src1));
-        ggml_backend_tensor_get(src1, m_src1_data.data(), 0, ggml_nbytes(src1));
+        auto nbytes = ggml_nbytes(src1);
+        m_src1_data.resize(nbytes);
+        ggml_backend_tensor_get(src1, m_src1_data.data(), 0, nbytes);
     }
 
-    const float * data = is_host ? (const float *) src1->data : m_src1_data.data();
+    const float * data = is_host ? (const float *) src1->data : (const float *)m_src1_data.data();
 
     if (m_collect_lsim) {
         if (wname.find(".ffn_") != std::string::npos) {
@@ -331,25 +332,38 @@ bool IMatrixCollector::collect_imatrix(struct ggml_tensor * t, bool ask, void *
         }
         auto & e = m_stats[wname];
         if (e.values.empty()) {
-            e.values.resize(src1->ne[0], 0);
-            e.counts.resize(src1->ne[0], 0);
+            if (src0->ne[3] > 1) {
+                fprintf(stderr, "Unsupported 4D tensor %s\n", wname.c_str());
+                exit(1);
+            }
+            // If we have a 3D tensor as it is the case for the attn_k_b and attn_v_b for DeepSeek MLA models,
+            // than we need to compute the imatrix for each head, and not just one imatrx for all heads.
+            // Hence, the storage we need is src0->ne[0]*src0->ne[2].
+            e.values.resize(src0->ne[0]*src0->ne[2], 0);
+            e.counts.resize(src0->ne[0]*src0->ne[2], 0);
         }
-        else if (e.values.size() != (size_t)src1->ne[0]) {
+        else if (e.values.size() != (size_t)(src0->ne[0]*src0->ne[2])) {
             fprintf(stderr, "Oops: inconsistent size for %s (%d vs %d)\n", wname.c_str(), (int)e.values.size(), (int)src1->ne[0]);
             exit(1); //GGML_ABORT("fatal error");
         }
         ++e.ncall;
         if (m_params.verbosity > 1) {
             printf("%s[%d]: %32s, %s, %5d x %5d, %d\n", __func__, m_last_call, wname.c_str(), ggml_op_name(t->op), (int)src1->ne[0], (int)src1->ne[1], (int)src1->type);
         }
-        for (int row = 0; row < (int)(src1->ne[1]*src1->ne[2]); ++row) {
-            const float * x = data + row * src1->ne[0];
-            for (int j = 0; j < (int)src1->ne[0]; ++j) {
-                e.values[j] += x[j]*x[j];
-                e.counts[j]++;
-                if (!std::isfinite(e.values[j])) {
-                    fprintf(stderr, "%f detected in %s\n", e.values[j], wname.c_str());
-                    exit(1);
+        int rk2 = src1->ne[2]/src0->ne[2];
+        for (int i12 = 0; i12 < (int)src1->ne[2]; ++i12) {  // i.e., loop over attention heads for MLA models
+            int i02 = i12/rk2;
+            auto values = e.values.data() + i02*src0->ne[0];
+            auto counts = e.counts.data() + i02*src0->ne[0];
+            for (int i11 = 0; i11 < (int)src1->ne[1]; ++i11) {
+                const float * x = (const float *)((const char *)data + i11*src1->nb[1] + i12*src1->nb[2]);
+                for (int j = 0; j < (int)src1->ne[0]; ++j) {
+                    values[j] += x[j]*x[j];
+                    counts[j]++;
+                    if (!std::isfinite(values[j])) {
+                        fprintf(stderr, "%f detected in %s\n", e.values[j], wname.c_str());
+                        exit(1);
+                    }
                 }
             }
         }