Re: [PATCH net-next 1/2] net/smc: Introduce a specific sysctl for TEST_LINK time

[Tony Lu]

On Tue, Sep 20, 2022 at 10:53:54AM +0800, Wen Gu wrote:
> SMC-R tests the viability of link by sending out TEST_LINK LLC
> messages over RoCE fabric when connections on link have been
> idle for a time longer than keepalive interval (testlink time).
> 
> But using tcp_keepalive_time as testlink time maybe not quite
> suitable because it is default no less than two hours[1], which
> is too long for single link to find peer dead. The active host
> will still use peer-dead link (QP) sending messages, and can't
> find out until get IB_WC_RETRY_EXC_ERR error CQEs, which takes
> more time than TEST_LINK timeout (SMC_LLC_WAIT_TIME) normally.
> 
> So this patch introduces a independent sysctl for SMC-R to set
> link keepalive time, in order to detect link down in time. The
> default value is 30 seconds.
> 
> [1] https://www.rfc-editor.org/rfc/rfc1122#page-101
> 
> Signed-off-by: Wen Gu <guwen@xxxxxxxxxxxxxxxxx>

LGTM.

Reviewed-by: Tony Lu <tonylu@xxxxxxxxxxxxxxxxx>

> ---
>  Documentation/networking/smc-sysctl.rst |  7 +++++++
>  include/net/netns/smc.h                 |  1 +
>  net/smc/smc_llc.c                       |  2 +-
>  net/smc/smc_llc.h                       |  1 +
>  net/smc/smc_sysctl.c                    | 14 ++++++++++++++
>  5 files changed, 24 insertions(+), 1 deletion(-)
> 
> diff --git a/Documentation/networking/smc-sysctl.rst b/Documentation/networking/smc-sysctl.rst
> index 742e90e..f8c3d59 100644
> --- a/Documentation/networking/smc-sysctl.rst
> +++ b/Documentation/networking/smc-sysctl.rst
> @@ -34,3 +34,10 @@ smcr_buf_type - INTEGER
>          - 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. The maximum
> +	value is (INT_MAX / HZ) seconds, the minimum value is 1 second.
> +
> +	Default: 30 seconds.
> diff --git a/include/net/netns/smc.h b/include/net/netns/smc.h
> index 2adbe2b..d295e2c 100644
> --- a/include/net/netns/smc.h
> +++ b/include/net/netns/smc.h
> @@ -19,5 +19,6 @@ struct netns_smc {
>  #endif
>  	unsigned int			sysctl_autocorking_size;
>  	unsigned int			sysctl_smcr_buf_type;
> +	int				sysctl_smcr_testlink_time;
>  };
>  #endif
> diff --git a/net/smc/smc_llc.c b/net/smc/smc_llc.c
> index 175026a..388bd2e 100644
> --- a/net/smc/smc_llc.c
> +++ b/net/smc/smc_llc.c
> @@ -2127,7 +2127,7 @@ void smc_llc_lgr_init(struct smc_link_group *lgr, struct smc_sock *smc)
>  	init_waitqueue_head(&lgr->llc_flow_waiter);
>  	init_waitqueue_head(&lgr->llc_msg_waiter);
>  	mutex_init(&lgr->llc_conf_mutex);
> -	lgr->llc_testlink_time = READ_ONCE(net->ipv4.sysctl_tcp_keepalive_time);
> +	lgr->llc_testlink_time = READ_ONCE(net->smc.sysctl_smcr_testlink_time) * HZ;
>  }
>  
>  /* called after lgr was removed from lgr_list */
> diff --git a/net/smc/smc_llc.h b/net/smc/smc_llc.h
> index 4404e52..1de9a29 100644
> --- a/net/smc/smc_llc.h
> +++ b/net/smc/smc_llc.h
> @@ -19,6 +19,7 @@
>  
>  #define SMC_LLC_WAIT_FIRST_TIME		(5 * HZ)
>  #define SMC_LLC_WAIT_TIME		(2 * HZ)
> +#define SMC_LLC_TESTLINK_DEFAULT_TIME	30
>  
>  enum smc_llc_reqresp {
>  	SMC_LLC_REQ,
> diff --git a/net/smc/smc_sysctl.c b/net/smc/smc_sysctl.c
> index 0613868..7f68520 100644
> --- a/net/smc/smc_sysctl.c
> +++ b/net/smc/smc_sysctl.c
> @@ -16,8 +16,12 @@
>  
>  #include "smc.h"
>  #include "smc_core.h"
> +#include "smc_llc.h"
>  #include "smc_sysctl.h"
>  
> +static int smcr_testlink_time_min = 1;
> +static int smcr_testlink_time_max = (INT_MAX / HZ);
> +
>  static struct ctl_table smc_table[] = {
>  	{
>  		.procname       = "autocorking_size",
> @@ -35,6 +39,15 @@
>  		.extra1		= SYSCTL_ZERO,
>  		.extra2		= SYSCTL_TWO,
>  	},
> +	{
> +		.procname	= "smcr_testlink_time",
> +		.data		= &init_net.smc.sysctl_smcr_testlink_time,
> +		.maxlen		= sizeof(int),
> +		.mode		= 0644,
> +		.proc_handler	= proc_dointvec_minmax,
> +		.extra1		= &smcr_testlink_time_min,
> +		.extra2		= &smcr_testlink_time_max,
> +	},
>  	{  }
>  };
>  
> @@ -60,6 +73,7 @@ int __net_init smc_sysctl_net_init(struct net *net)
>  
>  	net->smc.sysctl_autocorking_size = SMC_AUTOCORKING_DEFAULT_SIZE;
>  	net->smc.sysctl_smcr_buf_type = SMCR_PHYS_CONT_BUFS;
> +	net->smc.sysctl_smcr_testlink_time = SMC_LLC_TESTLINK_DEFAULT_TIME;
>  
>  	return 0;
>  
> -- 
> 1.8.3.1