[v6,net-next,0/5] Analyze and Reorganize core Networking Structs to optimize cacheline consumption

Message

Coco Li Oct. 30, 2023, 5:25 a.m. UTC

Currently, variable-heavy structs in the networking stack is organized
chronologically, logically and sometimes by cacheline access.

This patch series attempts to reorganize the core networking stack
variables to minimize cacheline consumption during the phase of data
transfer. Specifically, we looked at the TCP/IP stack and the fast
path definition in TCP.

For documentation purposes, we also added new files for each core data
structure we considered, although not all ended up being modified due
to the amount of existing cacheline they span in the fast path. In
the documentation, we recorded all variables we identified on the
fast path and the reasons. We also hope that in the future when
variables are added/modified, the document can be referred to and
updated accordingly to reflect the latest variable organization.

Tested:
Our tests were run with neper tcp_rr using tcp traffic. The tests have $cpu
number of threads and variable number of flows (see below).

Tests were run on 6.5-rc1

Efficiency is computed as cpu seconds / throughput (one tcp_rr round trip).
The following result shows efficiency delta before and after the patch
series is applied.

On AMD platforms with 100Gb/s NIC and 256Mb L3 cache:
IPv4
Flows   with patches    clean kernel      Percent reduction
30k     0.0001736538065 0.0002741191042 -36.65%
20k     0.0001583661752 0.0002712559158 -41.62%
10k     0.0001639148817 0.0002951800751 -44.47%
5k      0.0001859683866 0.0003320642536 -44.00%
1k      0.0002035190546 0.0003152056382 -35.43%

IPv6
Flows   with patches  clean kernel    Percent reduction
30k     0.000202535503  0.0003275329163 -38.16%
20k     0.0002020654777 0.0003411304786 -40.77%
10k     0.0002122427035 0.0003803674705 -44.20%
5k      0.0002348776729 0.0004030403953 -41.72%
1k      0.0002237384583 0.0002813646157 -20.48%

On Intel platforms with 200Gb/s NIC and 105Mb L3 cache:
IPv6
Flows   with patches    clean kernel    Percent reduction
30k     0.0006296537873 0.0006370427753 -1.16%
20k     0.0003451029365 0.0003628016076 -4.88%
10k     0.0003187646958 0.0003346835645 -4.76%
5k      0.0002954676348 0.000311807592  -5.24%
1k      0.0001909169342 0.0001848069709 3.31%

v5 changes:
1) removed snmp patch changes for next net-dev cycle. Pending work:
move file out of uapi.
2) updated cache group size requirements. Chosen to not use cachelines
but actual sum of struct member sizes to not make assumptions on cacheline
sizes.

v6 changes:
1) fixed one comment.

Coco Li (5):
  Documentations: Analyze heavily used Networking related structs
  cache: enforce cache groups
  netns-ipv4: reorganize netns_ipv4 fast path variables
  net-device: reorganize net_device fast path variables
  tcp: reorganize tcp_sock fast path variables

 Documentation/networking/index.rst            |   1 +
 .../networking/net_cachelines/index.rst       |  13 +
 .../net_cachelines/inet_connection_sock.rst   |  47 ++++
 .../networking/net_cachelines/inet_sock.rst   |  41 +++
 .../networking/net_cachelines/net_device.rst  | 175 ++++++++++++
 .../net_cachelines/netns_ipv4_sysctl.rst      | 155 +++++++++++
 .../networking/net_cachelines/snmp.rst        | 132 ++++++++++
 .../networking/net_cachelines/tcp_sock.rst    | 154 +++++++++++
 include/linux/cache.h                         |  25 ++
 include/linux/netdevice.h                     | 117 +++++----
 include/linux/tcp.h                           | 248 ++++++++++--------
 include/net/netns/ipv4.h                      |  47 ++--
 net/core/dev.c                                |  56 ++++
 net/core/net_namespace.c                      |  43 +++
 net/ipv4/tcp.c                                |  93 +++++++
 15 files changed, 1165 insertions(+), 182 deletions(-)
 create mode 100644 Documentation/networking/net_cachelines/index.rst
 create mode 100644 Documentation/networking/net_cachelines/inet_connection_sock.rst
 create mode 100644 Documentation/networking/net_cachelines/inet_sock.rst
 create mode 100644 Documentation/networking/net_cachelines/net_device.rst
 create mode 100644 Documentation/networking/net_cachelines/netns_ipv4_sysctl.rst
 create mode 100644 Documentation/networking/net_cachelines/snmp.rst
 create mode 100644 Documentation/networking/net_cachelines/tcp_sock.rst

Comments

Jakub Kicinski Oct. 30, 2023, 6:35 a.m. UTC | #1

On Mon, 30 Oct 2023 05:25:45 +0000 Coco Li wrote:
> Currently, variable-heavy structs in the networking stack is organized
> chronologically, logically and sometimes by cacheline access.

Merge window has started, see below. Also please take a look at our
process doc, specifically the 24h rule..

## Form letter - net-next-closed

The merge window for v6.7 has begun and we have already posted our pull
request. Therefore net-next is closed for new drivers, features, code
refactoring and optimizations. We are currently accepting bug fixes only.

Please repost when net-next reopens after Nov 12th.

RFC patches sent for review only are obviously welcome at any time.

See: https://www.kernel.org/doc/html/next/process/maintainer-netdev.html#development-cycle