diff --git a/Lib/asyncio/base_events.py b/Lib/asyncio/base_events.py
index c5ffad4..4505732 100644
--- a/Lib/asyncio/base_events.py
+++ b/Lib/asyncio/base_events.py
@@ -16,8 +16,10 @@
 
 import collections
 import concurrent.futures
+import functools
 import heapq
 import inspect
+import ipaddress
 import itertools
 import logging
 import os
@@ -70,49 +72,83 @@
         return repr(fd)
 
 
+# Linux's sock.type is a bitmask that can include extra info about socket.
+_SOCKET_TYPE_MASK = 0
+if hasattr(socket, 'SOCK_NONBLOCK'):
+    _SOCKET_TYPE_MASK |= socket.SOCK_NONBLOCK
+if hasattr(socket, 'SOCK_CLOEXEC'):
+    _SOCKET_TYPE_MASK |= socket.SOCK_CLOEXEC
+
+
+@functools.lru_cache(maxsize=1024)
+def _ipaddr_info(host, port, family, type, proto):
+    # Try to skip getaddrinfo if "host" is already an IP. Since getaddrinfo
+    # blocks on an exclusive lock on some platforms, users might handle name
+    # resolution in their own code and pass in resolved IPs.
+    if proto not in {0, socket.IPPROTO_TCP, socket.IPPROTO_UDP} or host is None:
+        return None
+
+    type &= ~_SOCKET_TYPE_MASK
+    if type == socket.SOCK_STREAM:
+        proto = socket.IPPROTO_TCP
+    elif type == socket.SOCK_DGRAM:
+        proto = socket.IPPROTO_UDP
+    else:
+        return None
+
+    if hasattr(socket, 'inet_pton'):
+        if family == socket.AF_UNSPEC:
+            afs = [socket.AF_INET, socket.AF_INET6]
+        else:
+            afs = [family]
+
+        for af in afs:
+            # Linux's inet_pton doesn't accept an IPv6 zone index after host,
+            # like '::1%lo0', so strip it. If we happen to make an invalid
+            # address look valid, we fail later in sock.connect or sock.bind.
+            try:
+                if af == socket.AF_INET6:
+                    socket.inet_pton(af, host.partition('%')[0])
+                else:
+                    socket.inet_pton(af, host)
+                return af, type, proto, '', (host, port)
+            except OSError:
+                pass
+
+        # "host" is not an IP address.
+        return None
+
+    # No inet_pton. (On Windows it's only available since Python 3.4.)
+    # Even though getaddrinfo with AI_NUMERICHOST would be non-blocking, it
+    # still requires a lock on some platforms, and waiting for that lock could
+    # block the event loop. Use ipaddress instead, it's just text parsing.
+    try:
+        addr = ipaddress.IPv4Address(host)
+    except ValueError:
+        try:
+            addr = ipaddress.IPv6Address(host.partition('%')[0])
+        except ValueError:
+            return None
+
+    af = socket.AF_INET if addr.version == 4 else socket.AF_INET6
+    if family not in (socket.AF_UNSPEC, af):
+        # "host" is wrong IP version for "family".
+        return None
+
+    return af, type, proto, '', (host, port)
+
+
 def _check_resolved_address(sock, address):
     # Ensure that the address is already resolved to avoid the trap of hanging
     # the entire event loop when the address requires doing a DNS lookup.
-    #
-    # getaddrinfo() is slow (around 10 us per call): this function should only
-    # be called in debug mode
-    family = sock.family
 
-    if family == socket.AF_INET:
-        host, port = address
-    elif family == socket.AF_INET6:
-        host, port = address[:2]
-    else:
+    if hasattr(socket, 'AF_UNIX') and sock.family == socket.AF_UNIX:
         return
 
-    # On Windows, socket.inet_pton() is only available since Python 3.4
-    if hasattr(socket, 'inet_pton'):
-        # getaddrinfo() is slow and has known issue: prefer inet_pton()
-        # if available
-        try:
-            socket.inet_pton(family, host)
-        except OSError as exc:
-            raise ValueError("address must be resolved (IP address), "
-                             "got host %r: %s"
-                             % (host, exc))
-    else:
-        # Use getaddrinfo(flags=AI_NUMERICHOST) to ensure that the address is
-        # already resolved.
-        type_mask = 0
-        if hasattr(socket, 'SOCK_NONBLOCK'):
-            type_mask |= socket.SOCK_NONBLOCK
-        if hasattr(socket, 'SOCK_CLOEXEC'):
-            type_mask |= socket.SOCK_CLOEXEC
-        try:
-            socket.getaddrinfo(host, port,
-                               family=family,
-                               type=(sock.type & ~type_mask),
-                               proto=sock.proto,
-                               flags=socket.AI_NUMERICHOST)
-        except socket.gaierror as err:
-            raise ValueError("address must be resolved (IP address), "
-                             "got host %r: %s"
-                             % (host, err))
+    host, port = address[:2]
+    if _ipaddr_info(host, port, sock.family, sock.type, sock.proto) is None:
+        raise ValueError("address must be resolved (IP address),"
+                         " got host %r" % host)
 
 
 def _run_until_complete_cb(fut):
@@ -535,7 +571,12 @@
 
     def getaddrinfo(self, host, port, *,
                     family=0, type=0, proto=0, flags=0):
-        if self._debug:
+        info = _ipaddr_info(host, port, family, type, proto)
+        if info is not None:
+            fut = futures.Future(loop=self)
+            fut.set_result([info])
+            return fut
+        elif self._debug:
             return self.run_in_executor(None, self._getaddrinfo_debug,
                                         host, port, family, type, proto, flags)
         else:
diff --git a/Lib/asyncio/proactor_events.py b/Lib/asyncio/proactor_events.py
index 7eac41e..14c0659 100644
--- a/Lib/asyncio/proactor_events.py
+++ b/Lib/asyncio/proactor_events.py
@@ -441,8 +441,7 @@
 
     def sock_connect(self, sock, address):
         try:
-            if self._debug:
-                base_events._check_resolved_address(sock, address)
+            base_events._check_resolved_address(sock, address)
         except ValueError as err:
             fut = futures.Future(loop=self)
             fut.set_exception(err)
diff --git a/Lib/asyncio/selector_events.py b/Lib/asyncio/selector_events.py
index a05f81c..5b26631 100644
--- a/Lib/asyncio/selector_events.py
+++ b/Lib/asyncio/selector_events.py
@@ -397,8 +397,7 @@
             raise ValueError("the socket must be non-blocking")
         fut = futures.Future(loop=self)
         try:
-            if self._debug:
-                base_events._check_resolved_address(sock, address)
+            base_events._check_resolved_address(sock, address)
         except ValueError as err:
             fut.set_exception(err)
         else:
diff --git a/Lib/asyncio/test_utils.py b/Lib/asyncio/test_utils.py
index 8170533..396e6ae 100644
--- a/Lib/asyncio/test_utils.py
+++ b/Lib/asyncio/test_utils.py
@@ -446,9 +446,14 @@
     finally:
         logger.setLevel(old_level)
 
-def mock_nonblocking_socket():
+
+def mock_nonblocking_socket(proto=socket.IPPROTO_TCP, type=socket.SOCK_STREAM,
+                            family=socket.AF_INET):
     """Create a mock of a non-blocking socket."""
-    sock = mock.Mock(socket.socket)
+    sock = mock.MagicMock(socket.socket)
+    sock.proto = proto
+    sock.type = type
+    sock.family = family
     sock.gettimeout.return_value = 0.0
     return sock