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Message-ID: <87y1g1b8jw.fsf@meer.lwn.net> Date: Tue, 17 Oct 2023 08:57:55 -0600 From: Jonathan Corbet <corbet@....net> To: Coco Li <lixiaoyan@...gle.com>, Jakub Kicinski <kuba@...nel.org>, Eric Dumazet <edumazet@...gle.com>, Neal Cardwell <ncardwell@...gle.com>, Mubashir Adnan Qureshi <mubashirq@...gle.com>, Paolo Abeni <pabeni@...hat.com> Cc: netdev@...r.kernel.org, Chao Wu <wwchao@...gle.com>, Wei Wang <weiwan@...gle.com>, Coco Li <lixiaoyan@...gle.com> Subject: Re: [PATCH v2 net-next 1/5] Documentations: Analyze heavily used Networking related structs Coco Li <lixiaoyan@...gle.com> writes: > 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 unidirectionaly. 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). > > Note that the optimization is not cache line size dependent, we use > x86 as an example of improvements. > > 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 respective take 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, linux_mib > > Signed-off-by: Coco Li <lixiaoyan@...gle.com> > Suggested-by: Eric Dumazet <edumazet@...gle.com> > --- > .../net_cachelines/inet_connection_sock.rst | 42 +++++ > .../networking/net_cachelines/inet_sock.rst | 37 ++++ > .../networking/net_cachelines/net_device.rst | 167 ++++++++++++++++++ > .../net_cachelines/netns_ipv4_sysctl.rst | 151 ++++++++++++++++ > .../networking/net_cachelines/snmp.rst | 128 ++++++++++++++ > .../networking/net_cachelines/tcp_sock.rst | 148 ++++++++++++++++ So none of this changelog tells us anything about this documentation you are adding or what readers are supposed to gain from it. What are these files? What they are *not* is RST; you clearly have not tried a documentation build with these files in place. I would say that needs to be fixed, but I do wonder if this kind of information (to the extent that I understand what it is) isn't better placed in the source itself? If nothing else, I would expect it to have a somewhat higher chance of staying current that way. Thanks, jon
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