On 06. 08. 22, 16:41, Jiri Slaby wrote:
On 06. 08. 22, 13:24, Neal Cardwell wrote:
On Sat, Aug 6, 2022 at 6:02 AM Jiri Slaby <jirislaby@xxxxxxxxxx> wrote:
On 21. 07. 22, 22:44, Wei Wang wrote:
This reverts commit 4a41f453bedfd5e9cd040bad509d9da49feb3e2c.
This to-be-reverted commit was meant to apply a stricter rule for the
stack to enter pingpong mode. However, the condition used to check for
interactive session "before(tp->lsndtime, icsk->icsk_ack.lrcvtime)" is
jiffy based and might be too coarse, which delays the stack entering
pingpong mode.
We revert this patch so that we no longer use the above condition to
determine interactive session, and also reduce pingpong threshold to 1.
Fixes: 4a41f453bedf ("tcp: change pingpong threshold to 3")
Reported-by: LemmyHuang <hlm3280@xxxxxxx>
Suggested-by: Neal Cardwell <ncardwell@xxxxxxxxxx>
Signed-off-by: Wei Wang <weiwan@xxxxxxxxxx>
This breaks python-eventlet [1] (and was backported to stable trees):
________________ TestHttpd.test_018b_http_10_keepalive_framing
_________________
self = <tests.wsgi_test.TestHttpd
testMethod=test_018b_http_10_keepalive_framing>
def test_018b_http_10_keepalive_framing(self):
# verify that if an http/1.0 client sends connection:
keep-alive
# that we don't mangle the request framing if the app doesn't
read the request
def app(environ, start_response):
resp_body = {
'/1': b'first response',
'/2': b'second response',
'/3': b'third response',
}.get(environ['PATH_INFO'])
if resp_body is None:
resp_body = 'Unexpected path: ' + environ['PATH_INFO']
if six.PY3:
resp_body = resp_body.encode('latin1')
# Never look at wsgi.input!
start_response('200 OK', [('Content-type', 'text/plain')])
return [resp_body]
self.site.application = app
sock = eventlet.connect(self.server_addr)
req_body = b'GET /tricksy HTTP/1.1\r\n'
body_len = str(len(req_body)).encode('ascii')
sock.sendall(b'PUT /1 HTTP/1.0\r\nHost:
localhost\r\nConnection: keep-alive\r\n'
b'Content-Length: ' + body_len + b'\r\n\r\n' +
req_body)
result1 = read_http(sock)
self.assertEqual(b'first response', result1.body)
self.assertEqual(result1.headers_original.get('Connection'),
'keep-alive')
sock.sendall(b'PUT /2 HTTP/1.0\r\nHost:
localhost\r\nConnection: keep-alive\r\n'
b'Content-Length: ' + body_len + b'\r\nExpect:
100-continue\r\n\r\n')
# Client may have a short timeout waiting on that 100 Continue
# and basically immediately send its body
sock.sendall(req_body)
result2 = read_http(sock)
self.assertEqual(b'second response', result2.body)
self.assertEqual(result2.headers_original.get('Connection'),
'close')
> sock.sendall(b'PUT /3 HTTP/1.0\r\nHost:
localhost\r\nConnection: close\r\n\r\n')
tests/wsgi_test.py:648:
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
_ _ _ _
eventlet/greenio/base.py:407: in sendall
tail = self.send(data, flags)
eventlet/greenio/base.py:401: in send
return self._send_loop(self.fd.send, data, flags)
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
_ _ _ _
self = <eventlet.greenio.base.GreenSocket object at 0x7f5f2f73c9a0>
send_method = <built-in method send of socket object at 0x7f5f2f73d520>
data = b'PUT /3 HTTP/1.0\r\nHost: localhost\r\nConnection:
close\r\n\r\n'
args = (0,), _timeout_exc = timeout('timed out'), eno = 32
def _send_loop(self, send_method, data, *args):
if self.act_non_blocking:
return send_method(data, *args)
_timeout_exc = socket_timeout('timed out')
while True:
try:
> return send_method(data, *args)
E BrokenPipeError: [Errno 32] Broken pipe
eventlet/greenio/base.py:388: BrokenPipeError
====================
Reverting this revert on the top of 5.19 solves the issue.
Any ideas?
Interesting. This revert should return the kernel back to the delayed
ACK behavior it had for many years before May 2019 and Linux 5.1,
which contains the commit it is reverting:
4a41f453bedfd tcp: change pingpong threshold to 3
It sounds like perhaps this test you mention has an implicit
dependence on the timing of delayed ACKs.
A few questions:
Dunno. I am only an openSUSE kernel maintainer and this popped out at
me. Feel free to dig to eventlet's sources on your own :P.
Any updates on this or should I send a revert directly?
The "before() &&" part of the patch makes the difference. That is this diff:
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -172,9 +172,17 @@ static void tcp_event_data_sent(struct tcp_sock *tp,
* and it is a reply for ato after last received packet,
* increase pingpong count.
*/
- if (before(tp->lsndtime, icsk->icsk_ack.lrcvtime) &&
- (u32)(now - icsk->icsk_ack.lrcvtime) < icsk->icsk_ack.ato)
+ pr_info("%s: sk=%p (%llx:%x) now=%u lsndtime=%u lrcvtime=%u
ping=%u\n",
+ __func__, sk, sk->sk_addrpair, sk->sk_portpair, now,
+ tp->lsndtime, icsk->icsk_ack.lrcvtime,
+ inet_csk(sk)->icsk_ack.pingpong);
+ if (//before(tp->lsndtime, icsk->icsk_ack.lrcvtime) &&
+ (u32)(now - icsk->icsk_ack.lrcvtime) < icsk->icsk_ack.ato) {
inet_csk_inc_pingpong_cnt(sk);
+ pr_info("\tINC ping=%u before=%u\n",
+ inet_csk(sk)->icsk_ack.pingpong,
+ before(tp->lsndtime,
icsk->icsk_ack.lrcvtime));
+ }
tp->lsndtime = now;
}
makes it work again, and outputs this:
> TCP: tcp_event_data_sent: sk=00000000fd67cf8d
(100007f0100007f:e858b18b) now=4294902140 lsndtime=4294902140
lrcvtime=4294902140 ping=0
> TCP: tcp_event_data_sent: sk=00000000a4becf82
(100007f0100007f:8bb158e8) now=4294902143 lsndtime=4294902140
lrcvtime=4294902142 ping=0
> TCP: INC ping=1 before=1
> TCP: tcp_event_data_sent: sk=00000000fd67cf8d
(100007f0100007f:e858b18b) now=4294902145 lsndtime=4294902140
lrcvtime=4294902144 ping=0
> TCP: INC ping=1 before=1
> TCP: tcp_event_data_sent: sk=00000000fd67cf8d
(100007f0100007f:e858b18b) now=4294902147 lsndtime=4294902145
lrcvtime=4294902144 ping=1
> TCP: INC ping=2 before=0
IMO, this "before=0" is the "source" of the problem. But I have no idea
what this means at all...
> TCP: tcp_event_data_sent: sk=00000000a4becf82
(100007f0100007f:8bb158e8) now=4294902149 lsndtime=4294902143
lrcvtime=4294902148 ping=1
> TCP: INC ping=2 before=1
> TCP: tcp_event_data_sent: sk=00000000fd67cf8d
(100007f0100007f:e858b18b) now=4294902151 lsndtime=4294902147
lrcvtime=4294902150 ping=3
> TCP: INC ping=4 before=1
> TCP: tcp_event_data_sent: sk=00000000c7a417e9
(100007f0100007f:e85ab18b) now=4294902153 lsndtime=4294902153
lrcvtime=4294902153 ping=0
> TCP: tcp_event_data_sent: sk=000000008681183e
(100007f0100007f:8bb15ae8) now=4294902155 lsndtime=4294902153
lrcvtime=4294902154 ping=0
> TCP: INC ping=1 before=1
(1) What are the timeout values in this test? If there is some
implicit or explicit timeout value less than the typical Linux TCP
40ms delayed ACK timer value then this could be the problem. If you
make sure all timeouts are at least, say, 300ms then this should
remove dependencies on delayed ACK behavior (and make the test more
portable).
(2) Does this test use the TCP_NODELAY socket option to disable
Nagle's algorithm? Presumably it should, given that it's a network app
that cares about latency. Omitting the TCP_NODELAY socket option can
cause request/response traffic to depend on delayed ACK behavior.
(3) If (1) and (2) do not fix the test, would you be able to provide
binary .pcap traces of the behavior with the test (a) passing and (b)
failing? For example:
sudo tcpdump -i any -w /tmp/trace.pcap -s 100 port 80 &
# run test
killall tcpdump
thanks,
neal
thanks,
--
js
suse labs
