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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 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: 64KiB
rmem - INTEGER
Initial size of receive buffer (RMB) used by SMC sockets.
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: 64KiB
smcr_max_links_per_lgr - INTEGER
Controls the max number of links can be added to a SMC-R link group. Notice that
the actual number of the links added to a SMC-R link group depends on the number
of RDMA devices exist in the system. The acceptable value ranges from 1 to 2. Only
for SMC-R v2.1 and later.
Default: 2
smcr_max_conns_per_lgr - INTEGER
Controls the max number of connections can be added to a SMC-R link group. The
acceptable value ranges from 16 to 255. Only for SMC-R v2.1 and later.
Default: 255
smcr_max_send_wr - INTEGER
So-called work request buffers are SMCR link (and RDMA queue pair) level
resources necessary for performing RDMA operations. Since up to 255
connections can share a link group and thus also a link and the number
of the work request buffers is decided when the link is allocated,
depending on the workload it can be a bottleneck in a sense that threads
have to wait for work request buffers to become available. Before the
introduction of this control the maximal number of work request buffers
available on the send path used to be hard coded to 16. With this control
it becomes configurable. The acceptable range is between 2 and 2048.
Please be aware that all the buffers need to be allocated as a physically
continuous array in which each element is a single buffer and has the size
of SMC_WR_BUF_SIZE (48) bytes. If the allocation fails, we keep retrying
with half of the buffer count until it is ether successful or (unlikely)
we dip below the old hard coded value which is 16 where we give up much
like before having this control.
Default: 16
smcr_max_recv_wr - INTEGER
So-called work request buffers are SMCR link (and RDMA queue pair) level
resources necessary for performing RDMA operations. Since up to 255
connections can share a link group and thus also a link and the number
of the work request buffers is decided when the link is allocated,
depending on the workload it can be a bottleneck in a sense that threads
have to wait for work request buffers to become available. Before the
introduction of this control the maximal number of work request buffers
available on the receive path used to be hard coded to 16. With this control
it becomes configurable. The acceptable range is between 2 and 2048.
Please be aware that all the buffers need to be allocated as a physically
continuous array in which each element is a single buffer and has the size
of SMC_WR_BUF_SIZE (48) bytes. If the allocation fails, we keep retrying
with half of the buffer count until it is ether successful or (unlikely)
we dip below the old hard coded value which is 16 where we give up much
like before having this control.
Default: 48
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