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net/smc: add sysctl for autocorking
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This add a new sysctl: net.smc.autocorking_size

We can dynamically change the behaviour of autocorking
by change the value of autocorking_size.
Setting to 0 disables autocorking in SMC

Signed-off-by: Dust Li <dust.li@linux.alibaba.com>
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Dust Li authored and intel-lab-lkp committed Mar 1, 2022
1 parent f1e9097 commit e00cb05
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Showing 4 changed files with 35 additions and 1 deletion.
23 changes: 23 additions & 0 deletions Documentation/networking/smc-sysctl.rst
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@@ -0,0 +1,23 @@
.. 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
1 change: 1 addition & 0 deletions include/net/netns/smc.h
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Expand Up @@ -17,5 +17,6 @@ struct netns_smc {
#ifdef CONFIG_SYSCTL
struct ctl_table_header *smc_hdr;
#endif
unsigned int sysctl_autocorking_size;
};
#endif
10 changes: 10 additions & 0 deletions net/smc/smc_sysctl.c
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Expand Up @@ -14,9 +14,17 @@
#include <linux/sysctl.h>
#include <net/net_namespace.h>

#include "smc.h"
#include "smc_sysctl.h"

static struct ctl_table smc_table[] = {
{
.procname = "autocorking_size",
.data = &init_net.smc.sysctl_autocorking_size,
.maxlen = sizeof(unsigned int),
.mode = 0644,
.proc_handler = proc_douintvec,
},
{ }
};

Expand All @@ -40,6 +48,8 @@ static __net_init int smc_sysctl_init_net(struct net *net)
if (!net->smc.smc_hdr)
goto err_reg;

net->smc.sysctl_autocorking_size = SMC_AUTOCORKING_DEFAULT_SIZE;

return 0;

err_reg:
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2 changes: 1 addition & 1 deletion net/smc/smc_tx.c
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Expand Up @@ -147,7 +147,7 @@ static bool smc_should_autocork(struct smc_sock *smc)
struct smc_connection *conn = &smc->conn;
int corking_size;

corking_size = min(SMC_AUTOCORKING_DEFAULT_SIZE,
corking_size = min(sock_net(&smc->sk)->smc.sysctl_autocorking_size,
conn->sndbuf_desc->len >> 1);

if (atomic_read(&conn->cdc_pend_tx_wr) == 0 ||
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