Date:   Tue, 23 Jan 2018 15:10:41 -0800
From:   Ben Greear <greearb@...delatech.com>
To:     Eric Dumazet <eric.dumazet@...il.com>,
        netdev <netdev@...r.kernel.org>
Subject: Re: TCP many-connection regression (bisected to 4.5.0-rc2+)

On 01/23/2018 02:29 PM, Eric Dumazet wrote:
> On Tue, 2018-01-23 at 14:09 -0800, Ben Greear wrote:
>> On 01/23/2018 02:07 PM, Eric Dumazet wrote:
>>> On Tue, 2018-01-23 at 13:49 -0800, Ben Greear wrote:
>>>> On 01/22/2018 10:16 AM, Eric Dumazet wrote:
>>>>> On Mon, 2018-01-22 at 09:28 -0800, Ben Greear wrote:
>>>>>> My test case is to have 6 processes each create 5000 TCP IPv4 connections to each other
>>>>>> on a system with 16GB RAM and send slow-speed data.  This works fine on a 4.7 kernel, but
>>>>>> will not work at all on a 4.13.  The 4.13 first complains about running out of tcp memory,
>>>>>> but even after forcing those values higher, the max connections we can get is around 15k.
>>>>>>
>>>>>> Both kernels have my out-of-tree patches applied, so it is possible it is my fault
>>>>>> at this point.
>>>>>>
>>>>>> Any suggestions as to what this might be caused by, or if it is fixed in more recent kernels?
>>>>>>
>>>>>> I will start bisecting in the meantime...
>>>>>>
>>>>>
>>>>> Hi Ben
>>>>>
>>>>> Unfortunately I have no idea.
>>>>>
>>>>> Are you using loopback flows, or have I misunderstood you ?
>>>>>
>>>>> How loopback connections can be slow-speed ?
>>>>>
>>>>
>>>> Hello Eric, looks like it is one of your commits that causes the issue
>>>> I see.
>>>>
>>>> Here are some more details on my specific test case I used to bisect:
>>>>
>>>> I have two ixgbe ports looped back, configured on same subnet, but with different IPs.
>>>> Routing table rules, SO_BINDTODEVICE, binding to specific IPs on both client and server
>>>> side let me send-to-self over the external looped cable.
>>>>
>>>> I have 2 mac-vlans on each physical interface.
>>>>
>>>> I created 5 server-side connections on one physical port, and two more on one of the mac-vlans.
>>>>
>>>> On the client-side, I create a process that spawns 5000 connections to the corresponding server side.
>>>>
>>>> End result is 25,000 connections on one pair of real interfaces, and 10,000 connections on the
>>>> mac-vlan ports.
>>>>
>>>> In the passing case, I get very close to all 5000 connections on all endpoints quickly.
>>>>
>>>> In the failing case, I get a max of around 16k connections on the two physical ports.  The two mac-vlans have 10k connections
>>>> across them working reliably.  It seems to be an issue with 'connect' failing.
>>>>
>>>> connect(2074, {sa_family=AF_INET, sin_port=htons(33012), sin_addr=inet_addr("10.1.1.5")}, 16) = -1 EINPROGRESS (Operation now in progress)
>>>> socket(PF_INET, SOCK_STREAM, IPPROTO_IP) = 2075
>>>> fcntl(2075, F_GETFD)                    = 0
>>>> fcntl(2075, F_SETFD, FD_CLOEXEC)        = 0
>>>> setsockopt(2075, SOL_SOCKET, SO_BINDTODEVICE, "eth4\0\0\0\0\0\0\0\0\0\0\0\0", 16) = 0
>>>> setsockopt(2075, SOL_SOCKET, SO_REUSEADDR, [1], 4) = 0
>>>> bind(2075, {sa_family=AF_INET, sin_port=htons(0), sin_addr=inet_addr("10.1.1.4")}, 16) = 0
>>>> getsockopt(2075, SOL_SOCKET, SO_RCVBUF, [87380], [4]) = 0
>>>> getsockopt(2075, SOL_SOCKET, SO_SNDBUF, [16384], [4]) = 0
>>>> setsockopt(2075, SOL_TCP, TCP_NODELAY, [0], 4) = 0
>>>> fcntl(2075, F_GETFL)                    = 0x2 (flags O_RDWR)
>>>> fcntl(2075, F_SETFL, O_ACCMODE|O_NONBLOCK) = 0
>>>> connect(2075, {sa_family=AF_INET, sin_port=htons(33012), sin_addr=inet_addr("10.1.1.5")}, 16) = -1 EINPROGRESS (Operation now in progress)
>>>> socket(PF_INET, SOCK_STREAM, IPPROTO_IP) = 2076
>>>> fcntl(2076, F_GETFD)                    = 0
>>>> fcntl(2076, F_SETFD, FD_CLOEXEC)        = 0
>>>> setsockopt(2076, SOL_SOCKET, SO_BINDTODEVICE, "eth4\0\0\0\0\0\0\0\0\0\0\0\0", 16) = 0
>>>> setsockopt(2076, SOL_SOCKET, SO_REUSEADDR, [1], 4) = 0
>>>> bind(2076, {sa_family=AF_INET, sin_port=htons(0), sin_addr=inet_addr("10.1.1.4")}, 16) = 0
>>>> getsockopt(2076, SOL_SOCKET, SO_RCVBUF, [87380], [4]) = 0
>>>> getsockopt(2076, SOL_SOCKET, SO_SNDBUF, [16384], [4]) = 0
>>>> setsockopt(2076, SOL_TCP, TCP_NODELAY, [0], 4) = 0
>>>> fcntl(2076, F_GETFL)                    = 0x2 (flags O_RDWR)
>>>> fcntl(2076, F_SETFL, O_ACCMODE|O_NONBLOCK) = 0
>>>> connect(2076, {sa_family=AF_INET, sin_port=htons(33012), sin_addr=inet_addr("10.1.1.5")}, 16) = -1 EADDRNOTAVAIL (Cannot assign requested address)
>>>> ....
>>>>
>>>>
>>>> ea8add2b190395408b22a9127bed2c0912aecbc8 is the first bad commit
>>>> commit ea8add2b190395408b22a9127bed2c0912aecbc8
>>>> Author: Eric Dumazet <edumazet@...gle.com>
>>>> Date:   Thu Feb 11 16:28:50 2016 -0800
>>>>
>>>>      tcp/dccp: better use of ephemeral ports in bind()
>>>>
>>>>      Implement strategy used in __inet_hash_connect() in opposite way :
>>>>
>>>>      Try to find a candidate using odd ports, then fallback to even ports.
>>>>
>>>>      We no longer disable BH for whole traversal, but one bucket at a time.
>>>>      We also use cond_resched() to yield cpu to other tasks if needed.
>>>>
>>>>      I removed one indentation level and tried to mirror the loop we have
>>>>      in __inet_hash_connect() and variable names to ease code maintenance.
>>>>
>>>>      Signed-off-by: Eric Dumazet <edumazet@...gle.com>
>>>>      Signed-off-by: David S. Miller <davem@...emloft.net>
>>>>
>>>> :040000 040000 3af4595c6eb6d331e1cba78a142d44e00f710d81 e0c014ae8b7e2867256eff60f6210821d36eacef M	net
>>>>
>>>>
>>>> I will be happy to test patches or try to get any other results that might help diagnose
>>>> this problem better.
>>>
>>> Problem is I do not see anything obvious here.
>>>
>>> Please provide /proc/sys/net/ipv4/ip_local_port_range
>>
>> [root@...003-e3v2-13100124-f20x64 ~]# cat /proc/sys/net/ipv4/ip_local_port_range
>> 10000	61001
>>
>>>
>>> Also you probably could use IP_BIND_ADDRESS_NO_PORT socket option
>>> before the bind()
>>
>> I'll read up on that to see what it does...
>
> man 7 ip
>
>        IP_BIND_ADDRESS_NO_PORT (since Linux 4.2)
>               Inform
> the kernel to not reserve an ephemeral  port
>               when  using
> bind(2)  with a port number of 0.  The
>               port will later be
> automatically  chosen  at  con‐
>               nect(2) time, in a way
> that allows sharing a source
>               port as long as the 4-tuple
> is unique.
>

Yes, I found that.

It appears this option works well for my case, and I see 30k connections across my pair of e1000e
(though the NIC is wretching again, so I guess its issues are not fully resolved).

I tested this on my 4.13.16+ kernel.

But that said, maybe there is still some issue with the patch I bisected to, so if you have
other suggestions, I can back out this IP_BIND_ADDRESS_NO_PORT feature and re-test.

Also, I had to increase /proc/sys/net/ipv4/tcp_mem to get 30k connections to work without
the kernel spamming:

Jan 23 15:02:41 lf1003-e3v2-13100124-f20x64 kernel: TCP: out of memory -- consider tuning tcp_mem
Jan 23 15:02:41 lf1003-e3v2-13100124-f20x64 kernel: TCP: out of memory -- consider tuning tcp_mem

This is a 16 GB RAM system, and I did not have to tune this on the 4.5.0-rc2+ (good) kernels
to get the similar performance.  I was testing on ixgbe there though, possibly that is part
of it, or maybe I just need to force tcp_mem to be larger on more recent kernels??

Thanks,
Ben


-- 
Ben Greear <greearb@...delatech.com>
Candela Technologies Inc  http://www.candelatech.com

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