netdev - Re: [PATCH v8 net-next 1/5] Documentations: Analyze heavily used Networking related structs

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Message-ID: <20231202195922.a3ekbrdfgqzfm6al@google.com>
Date: Sat, 2 Dec 2023 20:00:56 +0000
From: Shakeel Butt <shakeelb@...gle.com>
To: Coco Li <lixiaoyan@...gle.com>
Cc: 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>, Andrew Lunn <andrew@...n.ch>, Jonathan Corbet <corbet@....net>, 
	David Ahern <dsahern@...nel.org>, Daniel Borkmann <daniel@...earbox.net>, netdev@...r.kernel.org, 
	Chao Wu <wwchao@...gle.com>, Wei Wang <weiwan@...gle.com>, 
	Pradeep Nemavat <pnemavat@...gle.com>
Subject: Re: [PATCH v8 net-next 1/5] Documentations: Analyze heavily used
 Networking related structs

On Wed, Nov 29, 2023 at 07:27:52AM +0000, Coco Li wrote:
> 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 

We plan to reorganize?

> 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
> 

Is there any hidden meaning behind the capital I and N for
Inet_connection_sock and Netns_ipv4?

> 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: Eric Dumazet <edumazet@...gle.com>
> Signed-off-by: Coco Li <lixiaoyan@...gle.com>

Reviewed-by: Shakeel Butt <shakeelb@...gle.com>

This is really awesome work and motivated me to do something similar for
struct mem_cgroup (and or mm structs) as well.