Reduce the number of Send requests over UDS per IPC invocation

We sent up to 3 separate send requests over a socket. Now combine
then into one sendmgs() to improve performance and thread scheduling.

This improves PDX/UDS performance by up to 2x in some cases.

Bug: 65379030
Test: Sailfish works normally. Was able to run VR apps.
Change-Id: I00734d2c3f06d7d42b089569a8cc11c2273a1b7f

3 files changed, 50 insertions, 34 deletions

diff --git a/libs/vr/libpdx_uds/client_channel.cpp b/libs/vr/libpdx_uds/client_channel.cpp
index 9d9161784a..3f785fa62e 100644
--- a/libs/vr/libpdx_uds/client_channel.cpp
+++ b/libs/vr/libpdx_uds/client_channel.cpp
@@ -90,10 +90,12 @@ Status<void> SendRequest(const BorrowedHandle& socket_fd,
   size_t send_len = CountVectorSize(send_vector, send_count);
   InitRequest(&transaction_state->request, opcode, send_len, max_recv_len,
               false);
-  auto status = SendData(socket_fd, transaction_state->request);
-  if (status && send_len > 0)
-    status = SendDataVector(socket_fd, send_vector, send_count);
-  return status;
+  if (send_len == 0) {
+    send_vector = nullptr;
+    send_count = 0;
+  }
+  return SendData(socket_fd, transaction_state->request, send_vector,
+                  send_count);
 }
 
 Status<void> ReceiveResponse(const BorrowedHandle& socket_fd,
diff --git a/libs/vr/libpdx_uds/ipc_helper.cpp b/libs/vr/libpdx_uds/ipc_helper.cpp
index d75ce86e4b..f85b3bb666 100644
--- a/libs/vr/libpdx_uds/ipc_helper.cpp
+++ b/libs/vr/libpdx_uds/ipc_helper.cpp
@@ -20,6 +20,9 @@ namespace uds {
 
 namespace {
 
+constexpr size_t kMaxFdCount =
+    256;  // Total of 1KiB of data to transfer these FDs.
+
 // Default implementations of Send/Receive interfaces to use standard socket
 // send/sendmsg/recv/recvmsg functions.
 class SocketSender : public SendInterface {
@@ -175,20 +178,31 @@ Status<void> SendPayload::Send(const BorrowedHandle& socket_fd) {
 }
 
 Status<void> SendPayload::Send(const BorrowedHandle& socket_fd,
-                               const ucred* cred) {
+                               const ucred* cred, const iovec* data_vec,
+                               size_t vec_count) {
+  if (file_handles_.size() > kMaxFdCount) {
+    ALOGE(
+        "SendPayload::Send: Trying to send too many file descriptors (%zu), "
+        "max allowed = %zu",
+        file_handles_.size(), kMaxFdCount);
+    return ErrorStatus{EINVAL};
+  }
+
   SendInterface* sender = sender_ ? sender_ : &g_socket_sender;
   MessagePreamble preamble;
   preamble.magic = kMagicPreamble;
   preamble.data_size = buffer_.size();
   preamble.fd_count = file_handles_.size();
-  Status<void> ret = SendAll(sender, socket_fd, &preamble, sizeof(preamble));
-  if (!ret)
-    return ret;
 
   msghdr msg = {};
-  iovec recv_vect = {buffer_.data(), buffer_.size()};
-  msg.msg_iov = &recv_vect;
-  msg.msg_iovlen = 1;
+  msg.msg_iovlen = 2 + vec_count;
+  msg.msg_iov = static_cast<iovec*>(alloca(sizeof(iovec) * msg.msg_iovlen));
+  msg.msg_iov[0].iov_base = &preamble;
+  msg.msg_iov[0].iov_len = sizeof(preamble);
+  msg.msg_iov[1].iov_base = buffer_.data();
+  msg.msg_iov[1].iov_len = buffer_.size();
+  for (size_t i = 0; i < vec_count; i++)
+    msg.msg_iov[i + 2] = data_vec[i];
 
   if (cred || !file_handles_.empty()) {
     const size_t fd_bytes = file_handles_.size() * sizeof(int);
@@ -270,7 +284,15 @@ Status<void> ReceivePayload::Receive(const BorrowedHandle& socket_fd,
                                      ucred* cred) {
   RecvInterface* receiver = receiver_ ? receiver_ : &g_socket_receiver;
   MessagePreamble preamble;
-  Status<void> ret = RecvAll(receiver, socket_fd, &preamble, sizeof(preamble));
+  msghdr msg = {};
+  iovec recv_vect = {&preamble, sizeof(preamble)};
+  msg.msg_iov = &recv_vect;
+  msg.msg_iovlen = 1;
+  const size_t receive_fd_bytes = kMaxFdCount * sizeof(int);
+  msg.msg_controllen = CMSG_SPACE(sizeof(ucred)) + CMSG_SPACE(receive_fd_bytes);
+  msg.msg_control = alloca(msg.msg_controllen);
+
+  Status<void> ret = RecvMsgAll(receiver, socket_fd, &msg);
   if (!ret)
     return ret;
 
@@ -284,23 +306,6 @@ Status<void> ReceivePayload::Receive(const BorrowedHandle& socket_fd,
   file_handles_.clear();
   read_pos_ = 0;
 
-  msghdr msg = {};
-  iovec recv_vect = {buffer_.data(), buffer_.size()};
-  msg.msg_iov = &recv_vect;
-  msg.msg_iovlen = 1;
-
-  if (cred || preamble.fd_count) {
-    const size_t receive_fd_bytes = preamble.fd_count * sizeof(int);
-    msg.msg_controllen =
-        (cred ? CMSG_SPACE(sizeof(ucred)) : 0) +
-        (receive_fd_bytes == 0 ? 0 : CMSG_SPACE(receive_fd_bytes));
-    msg.msg_control = alloca(msg.msg_controllen);
-  }
-
-  ret = RecvMsgAll(receiver, socket_fd, &msg);
-  if (!ret)
-    return ret;
-
   bool cred_available = false;
   file_handles_.reserve(preamble.fd_count);
   cmsghdr* cmsg = CMSG_FIRSTHDR(&msg);
@@ -320,6 +325,10 @@ Status<void> ReceivePayload::Receive(const BorrowedHandle& socket_fd,
     cmsg = CMSG_NXTHDR(&msg, cmsg);
   }
 
+  ret = RecvAll(receiver, socket_fd, buffer_.data(), buffer_.size());
+  if (!ret)
+    return ret;
+
   if (cred && !cred_available) {
     ALOGE("ReceivePayload::Receive: Failed to obtain message credentials");
     ret.SetError(EIO);
diff --git a/libs/vr/libpdx_uds/private/uds/ipc_helper.h b/libs/vr/libpdx_uds/private/uds/ipc_helper.h
index bde16d3d31..664a0d1a1b 100644
--- a/libs/vr/libpdx_uds/private/uds/ipc_helper.h
+++ b/libs/vr/libpdx_uds/private/uds/ipc_helper.h
@@ -59,7 +59,8 @@ class SendPayload : public MessageWriter, public OutputResourceMapper {
  public:
   SendPayload(SendInterface* sender = nullptr) : sender_{sender} {}
   Status<void> Send(const BorrowedHandle& socket_fd);
-  Status<void> Send(const BorrowedHandle& socket_fd, const ucred* cred);
+  Status<void> Send(const BorrowedHandle& socket_fd, const ucred* cred,
+                    const iovec* data_vec = nullptr, size_t vec_count = 0);
 
   // MessageWriter
   void* GetNextWriteBufferSection(size_t size) override;
@@ -156,18 +157,22 @@ class ResponseHeader {
 };
 
 template <typename T>
-inline Status<void> SendData(const BorrowedHandle& socket_fd, const T& data) {
+inline Status<void> SendData(const BorrowedHandle& socket_fd, const T& data,
+                             const iovec* data_vec = nullptr,
+                             size_t vec_count = 0) {
   SendPayload payload;
   rpc::Serialize(data, &payload);
-  return payload.Send(socket_fd);
+  return payload.Send(socket_fd, nullptr, data_vec, vec_count);
 }
 
 template <typename FileHandleType>
 inline Status<void> SendData(const BorrowedHandle& socket_fd,
-                             const RequestHeader<FileHandleType>& request) {
+                             const RequestHeader<FileHandleType>& request,
+                             const iovec* data_vec = nullptr,
+                             size_t vec_count = 0) {
   SendPayload payload;
   rpc::Serialize(request, &payload);
-  return payload.Send(socket_fd, &request.cred);
+  return payload.Send(socket_fd, &request.cred, data_vec, vec_count);
 }
 
 Status<void> SendData(const BorrowedHandle& socket_fd, const void* data,