1.07x speedup: merge MQA parallel sections as suggested by @veluca93

PiperOrigin-RevId: 621772392

gemma.cc

@@ -405,18 +405,14 @@ HWY_NOINLINE void Attention(size_t batch_start, size_t batch_idx, size_t layer,
     });
   } else {
     // Multi-Query Attention
-    pool.Run(0, kHeads, [&](const uint64_t head, size_t /*thread*/) HWY_ATTR {
-      ProjQ(head, head * kQKVDim * kModelDim);
-    });
-
     constexpr const size_t q_offset = kHeads * kQKVDim * kModelDim;
     constexpr const size_t k_offset = q_offset + 0 * kQKVDim * kModelDim;
     constexpr const size_t v_offset = q_offset + 1 * kQKVDim * kModelDim;
     const size_t kv_offset = pos * kCachePosSize + layer * kCacheLayerSize;
-
     ProjKV(k_offset, v_offset, kv_offset);
 
     pool.Run(0, kHeads, [&](const uint64_t head, size_t /*thread*/) HWY_ATTR {
+      ProjQ(head, head * kQKVDim * kModelDim);
       Attn(head, 0);
     });
   }