diff --git a/changelog.d/6266.misc b/changelog.d/6266.misc
new file mode 100644
index 0000000000..634e421a79
--- /dev/null
+++ b/changelog.d/6266.misc
@@ -0,0 +1 @@
+Add benchmarks for structured logging and improve output performance.
diff --git a/synapse/logging/_terse_json.py b/synapse/logging/_terse_json.py
index 05fc64f409..03934956f4 100644
--- a/synapse/logging/_terse_json.py
+++ b/synapse/logging/_terse_json.py
@@ -256,6 +256,7 @@ class TerseJSONToTCPLogObserver(object):
             # transport is the same, just trigger a resumeProducing.
             if self._producer and r.transport is self._producer.transport:
                 self._producer.resumeProducing()
+                self._connection_waiter = None
                 return
 
             # If the producer is still producing, stop it.
diff --git a/synmark/__init__.py b/synmark/__init__.py
new file mode 100644
index 0000000000..570eb818d9
--- /dev/null
+++ b/synmark/__init__.py
@@ -0,0 +1,72 @@
+# -*- coding: utf-8 -*-
+# Copyright 2019 The Matrix.org Foundation C.I.C.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import sys
+
+from twisted.internet import epollreactor
+from twisted.internet.main import installReactor
+
+from synapse.config.homeserver import HomeServerConfig
+from synapse.util import Clock
+
+from tests.utils import default_config, setup_test_homeserver
+
+
+async def make_homeserver(reactor, config=None):
+    """
+    Make a Homeserver suitable for running benchmarks against.
+
+    Args:
+        reactor: A Twisted reactor to run under.
+        config: A HomeServerConfig to use, or None.
+    """
+    cleanup_tasks = []
+    clock = Clock(reactor)
+
+    if not config:
+        config = default_config("test")
+
+    config_obj = HomeServerConfig()
+    config_obj.parse_config_dict(config, "", "")
+
+    hs = await setup_test_homeserver(
+        cleanup_tasks.append, config=config_obj, reactor=reactor, clock=clock
+    )
+    stor = hs.get_datastore()
+
+    # Run the database background updates.
+    if hasattr(stor, "do_next_background_update"):
+        while not await stor.has_completed_background_updates():
+            await stor.do_next_background_update(1)
+
+    def cleanup():
+        for i in cleanup_tasks:
+            i()
+
+    return hs, clock.sleep, cleanup
+
+
+def make_reactor():
+    """
+    Instantiate and install a Twisted reactor suitable for testing (i.e. not the
+    default global one).
+    """
+    reactor = epollreactor.EPollReactor()
+
+    if "twisted.internet.reactor" in sys.modules:
+        del sys.modules["twisted.internet.reactor"]
+    installReactor(reactor)
+
+    return reactor
diff --git a/synmark/__main__.py b/synmark/__main__.py
new file mode 100644
index 0000000000..ac59befbd4
--- /dev/null
+++ b/synmark/__main__.py
@@ -0,0 +1,90 @@
+# -*- coding: utf-8 -*-
+# Copyright 2019 The Matrix.org Foundation C.I.C.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import sys
+from contextlib import redirect_stderr
+from io import StringIO
+
+import pyperf
+from synmark import make_reactor
+from synmark.suites import SUITES
+
+from twisted.internet.defer import ensureDeferred
+from twisted.logger import globalLogBeginner, textFileLogObserver
+from twisted.python.failure import Failure
+
+from tests.utils import setupdb
+
+
+def make_test(main):
+    """
+    Take a benchmark function and wrap it in a reactor start and stop.
+    """
+
+    def _main(loops):
+
+        reactor = make_reactor()
+
+        file_out = StringIO()
+        with redirect_stderr(file_out):
+
+            d = ensureDeferred(main(reactor, loops))
+
+            def on_done(_):
+                if isinstance(_, Failure):
+                    _.printTraceback()
+                    print(file_out.getvalue())
+                reactor.stop()
+                return _
+
+            d.addBoth(on_done)
+            reactor.run()
+
+        return d.result
+
+    return _main
+
+
+if __name__ == "__main__":
+
+    def add_cmdline_args(cmd, args):
+        if args.log:
+            cmd.extend(["--log"])
+
+    runner = pyperf.Runner(
+        processes=3, min_time=2, show_name=True, add_cmdline_args=add_cmdline_args
+    )
+    runner.argparser.add_argument("--log", action="store_true")
+    runner.parse_args()
+
+    orig_loops = runner.args.loops
+    runner.args.inherit_environ = ["SYNAPSE_POSTGRES"]
+
+    if runner.args.worker:
+        if runner.args.log:
+            globalLogBeginner.beginLoggingTo(
+                [textFileLogObserver(sys.__stdout__)], redirectStandardIO=False
+            )
+        setupdb()
+
+    for suite, loops in SUITES:
+        if loops:
+            runner.args.loops = loops
+        else:
+            runner.args.loops = orig_loops
+            loops = "auto"
+        runner.bench_time_func(
+            suite.__name__ + "_" + str(loops), make_test(suite.main),
+        )
diff --git a/synmark/suites/__init__.py b/synmark/suites/__init__.py
new file mode 100644
index 0000000000..cfa3b0ba38
--- /dev/null
+++ b/synmark/suites/__init__.py
@@ -0,0 +1,3 @@
+from . import logging
+
+SUITES = [(logging, 1000), (logging, 10000), (logging, None)]
diff --git a/synmark/suites/logging.py b/synmark/suites/logging.py
new file mode 100644
index 0000000000..d8e4c7d58f
--- /dev/null
+++ b/synmark/suites/logging.py
@@ -0,0 +1,118 @@
+# -*- coding: utf-8 -*-
+# Copyright 2019 The Matrix.org Foundation C.I.C.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import warnings
+from io import StringIO
+
+from mock import Mock
+
+from pyperf import perf_counter
+from synmark import make_homeserver
+
+from twisted.internet.defer import Deferred
+from twisted.internet.protocol import ServerFactory
+from twisted.logger import LogBeginner, Logger, LogPublisher
+from twisted.protocols.basic import LineOnlyReceiver
+
+from synapse.logging._structured import setup_structured_logging
+
+
+class LineCounter(LineOnlyReceiver):
+
+    delimiter = b"\n"
+
+    def __init__(self, *args, **kwargs):
+        self.count = 0
+        super().__init__(*args, **kwargs)
+
+    def lineReceived(self, line):
+        self.count += 1
+
+        if self.count >= self.factory.wait_for and self.factory.on_done:
+            on_done = self.factory.on_done
+            self.factory.on_done = None
+            on_done.callback(True)
+
+
+async def main(reactor, loops):
+    """
+    Benchmark how long it takes to send `loops` messages.
+    """
+    servers = []
+
+    def protocol():
+        p = LineCounter()
+        servers.append(p)
+        return p
+
+    logger_factory = ServerFactory.forProtocol(protocol)
+    logger_factory.wait_for = loops
+    logger_factory.on_done = Deferred()
+    port = reactor.listenTCP(0, logger_factory, interface="127.0.0.1")
+
+    hs, wait, cleanup = await make_homeserver(reactor)
+
+    errors = StringIO()
+    publisher = LogPublisher()
+    mock_sys = Mock()
+    beginner = LogBeginner(
+        publisher, errors, mock_sys, warnings, initialBufferSize=loops
+    )
+
+    log_config = {
+        "loggers": {"synapse": {"level": "DEBUG"}},
+        "drains": {
+            "tersejson": {
+                "type": "network_json_terse",
+                "host": "127.0.0.1",
+                "port": port.getHost().port,
+                "maximum_buffer": 100,
+            }
+        },
+    }
+
+    logger = Logger(namespace="synapse.logging.test_terse_json", observer=publisher)
+    logging_system = setup_structured_logging(
+        hs, hs.config, log_config, logBeginner=beginner, redirect_stdlib_logging=False
+    )
+
+    # Wait for it to connect...
+    await logging_system._observers[0]._service.whenConnected()
+
+    start = perf_counter()
+
+    # Send a bunch of useful messages
+    for i in range(0, loops):
+        logger.info("test message %s" % (i,))
+
+        if (
+            len(logging_system._observers[0]._buffer)
+            == logging_system._observers[0].maximum_buffer
+        ):
+            while (
+                len(logging_system._observers[0]._buffer)
+                > logging_system._observers[0].maximum_buffer / 2
+            ):
+                await wait(0.01)
+
+    await logger_factory.on_done
+
+    end = perf_counter() - start
+
+    logging_system.stop()
+    port.stopListening()
+    cleanup()
+
+    return end
diff --git a/tox.ini b/tox.ini
index 62b350ea6a..903a245fb0 100644
--- a/tox.ini
+++ b/tox.ini
@@ -102,6 +102,15 @@ commands =
 
     {envbindir}/coverage run "{envbindir}/trial"  {env:TRIAL_FLAGS:} {posargs:tests} {env:TOXSUFFIX:}
 
+[testenv:benchmark]
+deps =
+    {[base]deps}
+    pyperf
+setenv =
+    SYNAPSE_POSTGRES = 1
+commands =
+    python -m synmark {posargs:}
+
 [testenv:packaging]
 skip_install=True
 deps =