From 35ed1a65c6d69fc145939ebcc7c64ae4cc7da220 Mon Sep 17 00:00:00 2001
From: Brett Taylor <brtal@qti.qualcomm.com>
Date: Fri, 10 May 2024 18:07:35 -0700
Subject: [PATCH] Improve load time on serialized entries.

From profiling slow load times of serialized GPUv2 delegate data, a lot of unnecessary time is spent re-allocating memory as part of the call to std::string::append. By pre-allocating the correct size, we save a lot of time.

This patch was developed in 2022 (pardon the slow turn-around) and I no longer have the exact profiling details. However, my notes say that on an arbitrary but complex model, GetData() was previously taking 50ms; with this patch, it takes 18ms.
---
 tensorflow/lite/delegates/serialization.cc | 37 ++++++++++++++--------
 1 file changed, 23 insertions(+), 14 deletions(-)

diff --git a/tensorflow/lite/delegates/serialization.cc b/tensorflow/lite/delegates/serialization.cc
index 06ad487abf5a70..29791d78fca973 100644
--- a/tensorflow/lite/delegates/serialization.cc
+++ b/tensorflow/lite/delegates/serialization.cc
@@ -21,6 +21,7 @@ limitations under the License.
 #include <errno.h>
 #include <fcntl.h>
 #include <sys/file.h>
+#include <sys/stat.h>
 #include <unistd.h>
 
 #include <cstring>
@@ -193,22 +194,30 @@ TfLiteStatus SerializationEntry::GetData(TfLiteContext* context,
                        std::strerror(errno));
     return kTfLiteDelegateDataReadError;
   }
-  char buffer[512];
-  while (true) {
-    int bytes_read = read(fd, buffer, 512);
-    if (bytes_read == 0) {
-      // EOF
-      close(fd);
-      return kTfLiteOk;
-    } else if (bytes_read < 0) {
-      close(fd);
-      TF_LITE_KERNEL_LOG(context, "Error reading %s: %s", filepath.c_str(),
-                         std::strerror(errno));
-      return kTfLiteDelegateDataReadError;
-    } else {
-      data->append(buffer, bytes_read);
+
+  struct stat file_stat;
+  if (fstat(fd, &file_stat) < 0) {
+    close(fd);
+    TF_LITE_KERNEL_LOG(context, "Could not fstat %s: %s", filepath.c_str(),
+                       std::strerror(errno));
+    return kTfLiteDelegateDataReadError;
+  }
+  data->resize(file_stat.st_size);
+
+  size_t total_read = 0;
+  while (total_read < data->size()) {
+    ssize_t bytes_read = read(fd, data->data() + total_read, data->size() - total_read);
+    total_read += bytes_read;
+
+    if (bytes_read < 0) {
+        close(fd);
+        TF_LITE_KERNEL_LOG(context, "Error reading %s: %s", filepath.c_str(),
+                           std::strerror(errno));
+        return kTfLiteDelegateDataReadError;
     }
   }
+
+  close(fd);
 #endif  // defined(_WIN32)
 
   TFLITE_LOG_PROD(TFLITE_LOG_INFO,