getaddrinfo slowdown in 3.17.1, due to getifaddrs

["Steinar H. Gunderson" <sgunderson@bigfoot.com>]

Hi,

We recently upgraded a machine from 3.14.5 to 3.17.1, and a Perl script we're
running to poll SNMP suddenly needed ten times as much time to complete.
ps shows that it keeps being in state D (ie., I/O), and strace with -ttT
shows this curious pattern:

02:11:33.106973 socket(PF_NETLINK, SOCK_RAW, 0) = 42 <0.000013>
02:11:33.107013 bind(42, {sa_family=AF_NETLINK, pid=0, groups=00000000}, 12) = 0 <0.000010>
02:11:33.107051 getsockname(42, {sa_family=AF_NETLINK, pid=1128, groups=00000000}, [12]) = 0 <0.000008>
02:11:33.107094 sendto(42, "\24\0\0\0\26\0\1\3\265^@T\0\0\0\0\0\0\0\0", 20, 0, {sa_family=AF_NETLINK, pid=0, groups=00000000}, 12) = 20 <0.000015>
02:11:33.107146 recvmsg(42, {msg_name(12)={sa_family=AF_NETLINK, pid=0, groups=00000000}, msg_iov(1)=[{"L\0\0\0\24\0\2\0\265^@Th\4\0\0\2\10\200\376\1\0\0\0\10\0\1\0\177\0\0\1"..., 4096}], msg_controllen=0, msg_flags=0}, 0) = 332 <0.000016>
02:11:33.107208 recvmsg(42, {msg_name(12)={sa_family=AF_NETLINK, pid=0, groups=00000000}, msg_iov(1)=[{"H\0\0\0\24\0\2\0\265^@Th\4\0\0\n\200\200\376\1\0\0\0\24\0\1\0\0\0\0\0"..., 4096}], msg_controllen=0, msg_flags=0}, 0) = 936 <0.000010>
02:11:33.107262 recvmsg(42, {msg_name(12)={sa_family=AF_NETLINK, pid=0, groups=00000000}, msg_iov(1)=[{"\24\0\0\0\3\0\2\0\265^@Th\4\0\0\0\0\0\0\1\0\0\0\24\0\1\0\0\0\0\0"..., 4096}], msg_controllen=0, msg_flags=0}, 0) = 20 <0.000009>
02:11:33.107313 close(42)               = 0 <0.057092>
02:11:33.164529 open("/etc/hosts", O_RDONLY|O_CLOEXEC) = 42 <0.000080>
<more stuff...>

Debugging with gdb indicates that this is from getaddrinfo calls, which the
program (for, well, Perl reasons) uses as part of DNS reverse lookups.
getaddrinfo wants to look at the list of interfaces on the system
(__check_pf in glibc), which calls out to netlink via getifaddrs.
Note specifically the call to close(), which takes 57 ms to complete.

This doesn't happen on every single getaddrinfo call, but more like 50% of
them. I've tried on another machine, running 3.16.3, and we don't see
anything like it.

I've distilled it down to this Perl script:

  #! /usr/bin/perl
  use strict;
  use warnings;
  use Socket::GetAddrInfo;
  
  for my $i (1..1000) {
  	my ($err, @res) = Socket::GetAddrInfo::getaddrinfo("127.0.0.1", undef, { flags => Socket::GetAddrInfo::AI_NUMERICHOST });
  }

On my 3.16.3 machine, this completes in 26 ms. On the 3.17.1 machine:
65 _seconds_! According to the stack, this is what it's doing:

[<ffffffff810766b7>] wait_rcu_gp+0x48/0x4f
[<ffffffff81078be5>] synchronize_sched+0x29/0x2b
[<ffffffff813aacdb>] synchronize_net+0x19/0x1b
[<ffffffff813d313e>] netlink_release+0x25b/0x2b7
[<ffffffff8139af07>] sock_release+0x1a/0x79
[<ffffffff8139b1f4>] sock_close+0xd/0x11
[<ffffffff8111feca>] __fput+0xdf/0x184
[<ffffffff8111ff9f>] ____fput+0x9/0xb
[<ffffffff81051610>] task_work_run+0x7c/0x94
[<ffffffff810026b2>] do_notify_resume+0x55/0x66
[<ffffffff8146feda>] int_signal+0x12/0x17
[<ffffffffffffffff>] 0xffffffffffffffff

strace indicates it starts off nicely, then goes completely off:

cirkus:~> time strace -e close -ttT perl test.pl 
02:20:39.292060 close(3)                = 0 <0.000041>
02:20:39.292407 close(3)                = 0 <0.000037>
02:20:39.292660 close(3)                = 0 <0.000010>
02:20:39.292883 close(3)                = 0 <0.000009>
02:20:39.293100 close(3)                = 0 <0.000009>
[some more fast ones...]
02:20:39.311421 close(4)                = 0 <0.000009>
02:20:39.311927 close(3)                = 0 <0.000011>
02:20:39.312188 close(3)                = 0 <0.072224>
02:20:39.384979 close(3)                = 0 <0.059658>
02:20:39.445378 close(3)                = 0 <0.048205>
02:20:39.494213 close(3)                = 0 <0.060195>
^C

Is there a way to fix this? Somehow I doubt we're the only ones calling
getaddrinfo in this way. :-)

/* Steinar */
-- 
Homepage: http://www.sesse.net/