linux/Documentation/networking/smc-sysctl.rst
Tony Lu 0227f058aa net/smc: Unbind r/w buffer size from clcsock and make them tunable
Currently, SMC uses smc->sk.sk_{rcv|snd}buf to create buffers for
send buffer and RMB. And the values of buffer size are from tcp_{w|r}mem
in clcsock.

The buffer size from TCP socket doesn't fit SMC well. Generally, buffers
are usually larger than TCP for SMC-R/-D to get higher performance, for
they are different underlay devices and paths.

So this patch unbinds buffer size from TCP, and introduces two sysctl
knobs to tune them independently. Also, these knobs are per net
namespace and work for containers.

Signed-off-by: Tony Lu <tonylu@linux.alibaba.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
2022-09-22 12:58:21 +02:00

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.. SPDX-License-Identifier: GPL-2.0
==========
SMC Sysctl
==========
/proc/sys/net/smc/* Variables
=============================
autocorking_size - INTEGER
Setting SMC auto corking size:
SMC auto corking is like TCP auto corking from the application's
perspective of view. When applications do consecutive small
write()/sendmsg() system calls, we try to coalesce these small writes
as much as possible, to lower total amount of CDC and RDMA Write been
sent.
autocorking_size limits the maximum corked bytes that can be sent to
the under device in 1 single sending. If set to 0, the SMC auto corking
is disabled.
Applications can still use TCP_CORK for optimal behavior when they
know how/when to uncork their sockets.
Default: 64K
smcr_buf_type - INTEGER
Controls which type of sndbufs and RMBs to use in later newly created
SMC-R link group. Only for SMC-R.
Default: 0 (physically contiguous sndbufs and RMBs)
Possible values:
- 0 - Use physically contiguous buffers
- 1 - Use virtually contiguous buffers
- 2 - Mixed use of the two types. Try physically contiguous buffers first.
If not available, use virtually contiguous buffers then.
smcr_testlink_time - INTEGER
How frequently SMC-R link sends out TEST_LINK LLC messages to confirm
viability, after the last activity of connections on it. Value 0 means
disabling TEST_LINK.
Default: 30 seconds.
wmem - INTEGER
Initial size of send buffer used by SMC sockets.
The default value inherits from net.ipv4.tcp_wmem[1].
The minimum value is 16KiB and there is no hard limit for max value, but
only allowed 512KiB for SMC-R and 1MiB for SMC-D.
Default: 16K
rmem - INTEGER
Initial size of receive buffer (RMB) used by SMC sockets.
The default value inherits from net.ipv4.tcp_rmem[1].
The minimum value is 16KiB and there is no hard limit for max value, but
only allowed 512KiB for SMC-R and 1MiB for SMC-D.
Default: 128K