The more sockets we have in the hash table, the more time we spend
looking up the socket. While running a number of small workloads on
the same host, they penalise each other and cause performance degradation.
Also, the root cause might be a single workload that consumes much more
resources than the others. It often happens on a cloud service where
different workloads share the same computing resource.
On EC2 c5.24xlarge instance (196 GiB memory and 524288 (1Mi / 2) ehash
entries), after running iperf3 in different netns, creating 24Mi sockets
without data transfer in the root netns causes about 10% performance
regression for the iperf3's connection.
thash_entries sockets length Gbps
524288 1 1 50.7
24Mi 48 45.1
It is basically related to the length of the list of each hash bucket.
For testing purposes to see how performance drops along the length,
I set 131072 (1Mi / 8) to thash_entries, and here's the result.
thash_entries sockets length Gbps
131072 1 1 50.7
1Mi 8 49.9
2Mi 16 48.9
4Mi 32 47.3
8Mi 64 44.6
16Mi 128 40.6
24Mi 192 36.3
32Mi 256 32.5
40Mi 320 27.0
48Mi 384 25.0
To resolve the socket lookup degradation, we introduce an optional
per-netns hash table for TCP and UDP. With a smaller hash table, we
can look up sockets faster and isolate noisy neighbours. Also, we can
reduce lock contention.
We can control and check the hash size via sysctl knobs. It requires
some tuning based on workloads, so the per-netns hash table is disabled
by default.
# dmesg | cut -d ' ' -f 5- | grep "established hash"
TCP established hash table entries: 524288 (order: 10, 4194304 bytes, vmalloc hugepage)
# sysctl net.ipv4.tcp_ehash_entries
net.ipv4.tcp_ehash_entries = 524288 # can be changed by thash_entries
# sysctl net.ipv4.tcp_child_ehash_entries
net.ipv4.tcp_child_ehash_entries = 0 # disabled by default
# ip netns add test1
# ip netns exec test1 sysctl net.ipv4.tcp_ehash_entries
net.ipv4.tcp_ehash_entries = -524288 # share the global ehash
# sysctl -w net.ipv4.tcp_child_ehash_entries=100
net.ipv4.tcp_child_ehash_entries = 100
# sysctl net.ipv4.tcp_child_ehash_entries
net.ipv4.tcp_child_ehash_entries = 128 # rounded up to 2^n
# ip netns add test2
# ip netns exec test2 sysctl net.ipv4.tcp_ehash_entries
net.ipv4.tcp_ehash_entries = 128 # own per-netns ehash
[ UDP has the same interface as udp_hash_entries and
udp_child_hash_entries. ]
When creating per-netns concurrently with different sizes, we can
guarantee the size by doing one of these ways.
1) Share the global hash table and create per-netns one
First, unshare() with tcp_child_ehash_entries==0. It creates dedicated
netns sysctl knobs where we can safely change tcp_child_ehash_entries
and clone()/unshare() to create a per-netns hash table.
2) Lock the sysctl knob
We can use flock(LOCK_MAND) or BPF_PROG_TYPE_CGROUP_SYSCTL to allow/deny
read/write on sysctl knobs.
For details, please see each patch.
patch 1 - 3: mandatory lock support for sysctl (fs stuff)
patch 4 - 7: prep patch for per-netns TCP ehash
patch 8: add per-netns TCP ehash
patch 9 - 12: prep patch for per-netns UDP hash table
patch 13: add per-netns UDP hash table
Kuniyuki Iwashima (13):
fs/lock: Revive LOCK_MAND.
sysctl: Support LOCK_MAND for read/write.
selftest: sysctl: Add test for flock(LOCK_MAND).
net: Introduce init2() for pernet_operations.
tcp: Clean up some functions.
tcp: Set NULL to sk->sk_prot->h.hashinfo.
tcp: Access &tcp_hashinfo via net.
tcp: Introduce optional per-netns ehash.
udp: Clean up some functions.
udp: Set NULL to sk->sk_prot->h.udp_table.
udp: Set NULL to udp_seq_afinfo.udp_table.
udp: Access &udp_table via net.
udp: Introduce optional per-netns hash table.
Documentation/networking/ip-sysctl.rst | 40 +++++
.../chelsio/inline_crypto/chtls/chtls_cm.c | 5 +-
.../mellanox/mlx5/core/en_accel/ktls_rx.c | 5 +-
.../net/ethernet/netronome/nfp/crypto/tls.c | 5 +-
fs/locks.c | 83 ++++++---
fs/proc/proc_sysctl.c | 25 ++-
include/linux/fs.h | 1 +
include/net/inet_hashtables.h | 16 ++
include/net/net_namespace.h | 3 +
include/net/netns/ipv4.h | 4 +
include/uapi/asm-generic/fcntl.h | 5 -
net/core/filter.c | 9 +-
net/core/net_namespace.c | 18 +-
net/dccp/proto.c | 2 +
net/ipv4/af_inet.c | 2 +-
net/ipv4/esp4.c | 3 +-
net/ipv4/inet_connection_sock.c | 25 ++-
net/ipv4/inet_hashtables.c | 102 ++++++++---
net/ipv4/inet_timewait_sock.c | 4 +-
net/ipv4/netfilter/nf_socket_ipv4.c | 2 +-
net/ipv4/netfilter/nf_tproxy_ipv4.c | 17 +-
net/ipv4/sysctl_net_ipv4.c | 113 ++++++++++++
net/ipv4/tcp.c | 1 +
net/ipv4/tcp_diag.c | 18 +-
net/ipv4/tcp_ipv4.c | 122 +++++++++----
net/ipv4/tcp_minisocks.c | 2 +-
net/ipv4/udp.c | 164 ++++++++++++++----
net/ipv4/udp_diag.c | 6 +-
net/ipv4/udp_offload.c | 5 +-
net/ipv6/esp6.c | 3 +-
net/ipv6/inet6_hashtables.c | 4 +-
net/ipv6/netfilter/nf_socket_ipv6.c | 2 +-
net/ipv6/netfilter/nf_tproxy_ipv6.c | 5 +-
net/ipv6/tcp_ipv6.c | 30 +++-
net/ipv6/udp.c | 31 ++--
net/ipv6/udp_offload.c | 5 +-
net/mptcp/mptcp_diag.c | 7 +-
tools/testing/selftests/sysctl/.gitignore | 2 +
tools/testing/selftests/sysctl/Makefile | 9 +-
tools/testing/selftests/sysctl/sysctl_flock.c | 157 +++++++++++++++++
40 files changed, 854 insertions(+), 208 deletions(-)
create mode 100644 tools/testing/selftests/sysctl/.gitignore
create mode 100644 tools/testing/selftests/sysctl/sysctl_flock.c
--
2.30.2
