Commit 14006f1d authored by Coco Li's avatar Coco Li Committed by David S. Miller
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Documentations: Analyze heavily used Networking related structs 



Analyzed a few structs in the networking stack by looking at variables
within them that are used in the TCP/IP fast path.

Fast path is defined as TCP path where data is transferred from sender to
receiver unidirectionally. It doesn't include phases other than
TCP_ESTABLISHED, nor does it look at error paths.

We hope to re-organizing variables that span many cachelines whose fast
path variables are also spread out, and this document can help future
developers keep networking fast path cachelines small.

Optimized_cacheline field is computed as
(Fastpath_Bytes/L3_cacheline_size_x86), and not the actual organized
results (see patches to come for these).

Investigation is done on 6.5

Name	                Struct_Cachelines  Cur_fastpath_cache Fastpath_Bytes Optimized_cacheline
tcp_sock	        42 (2664 Bytes)	   12   		396		8
net_device	        39 (2240 bytes)	   12			234		4
inet_sock	        15 (960 bytes)	   14			922		14
Inet_connection_sock	22 (1368 bytes)	   18			1166		18
Netns_ipv4 (sysctls)	12 (768 bytes)     4			77		2
linux_mib	        16 (1060)	   6			104		2

Note how there isn't much improvement space for inet_sock and
Inet_connection_sock because sk and icsk_inet respectively takes up so
much of the struct that rest of the variables become a small portion of
the struct size.

So, we decided to reorganize tcp_sock, net_device, netns_ipv4

Suggested-by: default avatarEric Dumazet <edumazet@google.com>
Signed-off-by: default avatarCoco Li <lixiaoyan@google.com>
Reviewed-by: default avatarEric Dumazet <edumazet@google.com>
Reviewed-by: default avatarShakeel Butt <shakeelb@google.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 7453d7a6

Documentation/networking/index.rst

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@@ -75,6 +75,7 @@ Contents: 
   mptcp-sysctl

   multiqueue

   napi

   net_cachelines/index

   netconsole

   netdev-features

   netdevices

Documentation/networking/net_cachelines/index.rst

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.. SPDX-License-Identifier: GPL-2.0

.. Copyright (C) 2023 Google LLC

===================================

Common Networking Struct Cachelines

===================================



.. toctree::

   :maxdepth: 1



   inet_connection_sock

   inet_sock

   net_device

   netns_ipv4_sysctl

   snmp

   tcp_sock

Documentation/networking/net_cachelines/inet_connection_sock.rst

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.. SPDX-License-Identifier: GPL-2.0

.. Copyright (C) 2023 Google LLC

=====================================================

inet_connection_sock struct fast path usage breakdown

=====================================================



Type                                Name                   fastpath_tx_access  fastpath_rx_access  comment

..struct                            ..inet_connection_sock                                         

struct_inet_sock                    icsk_inet              read_mostly         read_mostly         tcp_init_buffer_space,tcp_init_transfer,tcp_finish_connect,tcp_connect,tcp_send_rcvq,tcp_send_syn_data

struct_request_sock_queue           icsk_accept_queue      -                   -                   

struct_inet_bind_bucket             icsk_bind_hash         read_mostly         -                   tcp_set_state

struct_inet_bind2_bucket            icsk_bind2_hash        read_mostly         -                   tcp_set_state,inet_put_port

unsigned_long                       icsk_timeout           read_mostly         -                   inet_csk_reset_xmit_timer,tcp_connect

struct_timer_list                   icsk_retransmit_timer  read_mostly         -                   inet_csk_reset_xmit_timer,tcp_connect

struct_timer_list                   icsk_delack_timer      read_mostly         -                   inet_csk_reset_xmit_timer,tcp_connect

u32                                 icsk_rto               read_write          -                   tcp_cwnd_validate,tcp_schedule_loss_probe,tcp_connect_init,tcp_connect,tcp_write_xmit,tcp_push_one

u32                                 icsk_rto_min           -                   -                   

u32                                 icsk_delack_max        -                   -                   

u32                                 icsk_pmtu_cookie       read_write          -                   tcp_sync_mss,tcp_current_mss,tcp_send_syn_data,tcp_connect_init,tcp_connect

struct_tcp_congestion_ops           icsk_ca_ops            read_write          -                   tcp_cwnd_validate,tcp_tso_segs,tcp_ca_dst_init,tcp_connect_init,tcp_connect,tcp_write_xmit

struct_inet_connection_sock_af_ops  icsk_af_ops            read_mostly         -                   tcp_finish_connect,tcp_send_syn_data,tcp_mtup_init,tcp_mtu_check_reprobe,tcp_mtu_probe,tcp_connect_init,tcp_connect,__tcp_transmit_skb

struct_tcp_ulp_ops*                 icsk_ulp_ops           -                   -                   

void*                               icsk_ulp_data          -                   -                   

u8:5                                icsk_ca_state          read_write          -                   tcp_cwnd_application_limited,tcp_set_ca_state,tcp_enter_cwr,tcp_tso_should_defer,tcp_mtu_probe,tcp_schedule_loss_probe,tcp_write_xmit,__tcp_transmit_skb

u8:1                                icsk_ca_initialized    read_write          -                   tcp_init_transfer,tcp_init_congestion_control,tcp_init_transfer,tcp_finish_connect,tcp_connect

u8:1                                icsk_ca_setsockopt     -                   -                   

u8:1                                icsk_ca_dst_locked     write_mostly        -                   tcp_ca_dst_init,tcp_connect_init,tcp_connect

u8                                  icsk_retransmits       write_mostly        -                   tcp_connect_init,tcp_connect

u8                                  icsk_pending           read_write          -                   inet_csk_reset_xmit_timer,tcp_connect,tcp_check_probe_timer,__tcp_push_pending_frames,tcp_rearm_rto,tcp_event_new_data_sent,tcp_event_new_data_sent

u8                                  icsk_backoff           write_mostly        -                   tcp_write_queue_purge,tcp_connect_init

u8                                  icsk_syn_retries       -                   -                   

u8                                  icsk_probes_out        -                   -                   

u16                                 icsk_ext_hdr_len       read_mostly         -                   __tcp_mtu_to_mss,tcp_mtu_to_rss,tcp_mtu_probe,tcp_write_xmit,tcp_mtu_to_mss,

struct_icsk_ack_u8                  pending                read_write          read_write          inet_csk_ack_scheduled,__tcp_cleanup_rbuf,tcp_cleanup_rbuf,inet_csk_clear_xmit_timer,tcp_event_ack-sent,inet_csk_reset_xmit_timer

struct_icsk_ack_u8                  quick                  read_write          write_mostly        tcp_dec_quickack_mode,tcp_event_ack_sent,__tcp_transmit_skb,__tcp_select_window,__tcp_cleanup_rbuf

struct_icsk_ack_u8                  pingpong               -                   -                   

struct_icsk_ack_u8                  retry                  write_mostly        read_write          inet_csk_clear_xmit_timer,tcp_rearm_rto,tcp_event_new_data_sent,tcp_write_xmit,__tcp_send_ack,tcp_send_ack,

struct_icsk_ack_u8                  ato                    read_mostly         write_mostly        tcp_dec_quickack_mode,tcp_event_ack_sent,__tcp_transmit_skb,__tcp_send_ack,tcp_send_ack

struct_icsk_ack_unsigned_long       timeout                read_write          read_write          inet_csk_reset_xmit_timer,tcp_connect

struct_icsk_ack_u32                 lrcvtime               read_write          -                   tcp_finish_connect,tcp_connect,tcp_event_data_sent,__tcp_transmit_skb

struct_icsk_ack_u16                 rcv_mss                write_mostly        read_mostly         __tcp_select_window,__tcp_cleanup_rbuf,tcp_initialize_rcv_mss,tcp_connect_init

struct_icsk_mtup_int                search_high            read_write          -                   tcp_mtup_init,tcp_sync_mss,tcp_connect_init,tcp_mtu_check_reprobe,tcp_write_xmit

struct_icsk_mtup_int                search_low             read_write          -                   tcp_mtu_probe,tcp_mtu_check_reprobe,tcp_write_xmit,tcp_sync_mss,tcp_connect_init,tcp_mtup_init

struct_icsk_mtup_u32:31             probe_size             read_write          -                   tcp_mtup_init,tcp_connect_init,__tcp_transmit_skb

struct_icsk_mtup_u32:1              enabled                read_write          -                   tcp_mtup_init,tcp_sync_mss,tcp_connect_init,tcp_mtu_probe,tcp_write_xmit

struct_icsk_mtup_u32                probe_timestamp        read_write          -                   tcp_mtup_init,tcp_connect_init,tcp_mtu_check_reprobe,tcp_mtu_probe

u32                                 icsk_probes_tstamp     -                   -                   

u32                                 icsk_user_timeout      -                   -                   

u64[104/sizeof(u64)]                icsk_ca_priv           -                   -

Documentation/networking/net_cachelines/inet_sock.rst

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.. SPDX-License-Identifier: GPL-2.0

.. Copyright (C) 2023 Google LLC

=====================================================

inet_connection_sock struct fast path usage breakdown

=====================================================



Type                    Name                  fastpath_tx_access  fastpath_rx_access  comment

..struct                ..inet_sock                                                     

struct_sock             sk                    read_mostly         read_mostly         tcp_init_buffer_space,tcp_init_transfer,tcp_finish_connect,tcp_connect,tcp_send_rcvq,tcp_send_syn_data

struct_ipv6_pinfo*      pinet6                -                   -                   

be16                    inet_sport            read_mostly         -                   __tcp_transmit_skb

be32                    inet_daddr            read_mostly         -                   ip_select_ident_segs

be32                    inet_rcv_saddr        -                   -                   

be16                    inet_dport            read_mostly         -                   __tcp_transmit_skb

u16                     inet_num              -                   -                   

be32                    inet_saddr            -                   -                   

s16                     uc_ttl                read_mostly         -                   __ip_queue_xmit/ip_select_ttl

u16                     cmsg_flags            -                   -                   

struct_ip_options_rcu*  inet_opt              read_mostly         -                   __ip_queue_xmit

u16                     inet_id               read_mostly         -                   ip_select_ident_segs

u8                      tos                   read_mostly         -                   ip_queue_xmit

u8                      min_ttl               -                   -                   

u8                      mc_ttl                -                   -                   

u8                      pmtudisc              -                   -                   

u8:1                    recverr               -                   -                   

u8:1                    is_icsk               -                   -                   

u8:1                    freebind              -                   -                   

u8:1                    hdrincl               -                   -                   

u8:1                    mc_loop               -                   -                   

u8:1                    transparent           -                   -                   

u8:1                    mc_all                -                   -                   

u8:1                    nodefrag              -                   -                   

u8:1                    bind_address_no_port  -                   -                   

u8:1                    recverr_rfc4884       -                   -                   

u8:1                    defer_connect         read_mostly         -                   tcp_sendmsg_fastopen

u8                      rcv_tos               -                   -                   

u8                      convert_csum          -                   -                   

int                     uc_index              -                   -                   

int                     mc_index              -                   -                   

be32                    mc_addr               -                   -                   

struct_ip_mc_socklist*  mc_list               -                   -                   

struct_inet_cork_full   cork                  read_mostly         -                   __tcp_transmit_skb

struct                  local_port_range      -                   -

Documentation/networking/net_cachelines/net_device.rst

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