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[Openvpn-devel,net-next,v2,0/2] ovpn: reduce reference-count contention

Message ID cover.1789746543.git.ralf@mandelbit.com
Headers
Series ovpn: reduce reference-count contention |

Message

Ralf Lici Sept. 18, 2026, 4:03 p.m. UTC 
  Hi,

Currently ovpn holds peer and key-slot references while packets are
being processed and until asynchronous crypto completes. With traffic
for one peer spread across CPUs, the shared kref cachelines therefore
become contended even though both objects are normally long-lived.

This series converts both references to percpu_ref while preserving their
existing RCU-delayed destruction. The individual patch messages describe
the memory cost and cache-to-cache measurements.

The test used one peer, one AES-128-GCM key and 32 TCP streams on a
32-logical-CPU Ryzen 9 9950X with a ConnectX-5 hairpin. The encrypted RX
flow used one source port and one receive queue, so only TX exercised CPU
fan-out. perf c2c showed that each shared reference cacheline disappeared
after its respective conversion.

Thanks,

Ralf Lici
Mandelbit Srl

---
Changes since v1 https://lore.kernel.org/openvpn-devel/cover.1789658051.git.ralf@mandelbit.com/
- In 1/2, distinguish reference acquisitions which extend existing peer
  ownership from RCU lookups which must reject dying peers. (Sashiko)
- In 2/2, avoid a nested RCU callback during key-slot release which
  could outlive the ovpn workqueue during module unload. (Sashiko)

Ralf Lici (2):
  ovpn: use percpu references for peers
  ovpn: use percpu references for key slots

 drivers/net/ovpn/crypto.c      | 16 +++++++--------
 drivers/net/ovpn/crypto.h      | 27 ++++++++++++++++++++-----
 drivers/net/ovpn/crypto_aead.c | 17 ++++++++++++----
 drivers/net/ovpn/io.c          |  6 +-----
 drivers/net/ovpn/netlink.c     |  6 +++---
 drivers/net/ovpn/peer.c        | 37 +++++++++++++++++++++-------------
 drivers/net/ovpn/peer.h        | 37 ++++++++++++++++++++++++++++------
 drivers/net/ovpn/tcp.c         | 23 ++++++++++-----------
 8 files changed, 112 insertions(+), 57 deletions(-)


base-commit: b8e9e7d82e7eefd5d2d528469d94ec20e96b38c3