linux-kernel - Re: [PATCH net-next v3 1/2] net/smc: make wr buffer count configurable

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Message-ID: <7cc2df09-0230-40cb-ad4f-656b0d1d785b@redhat.com>
Date: Thu, 25 Sep 2025 11:27:38 +0200
From: Paolo Abeni <pabeni@...hat.com>
To: Halil Pasic <pasic@...ux.ibm.com>, Jakub Kicinski <kuba@...nel.org>,
 Simon Horman <horms@...nel.org>, "D. Wythe" <alibuda@...ux.alibaba.com>,
 Dust Li <dust.li@...ux.alibaba.com>, Sidraya Jayagond
 <sidraya@...ux.ibm.com>, Wenjia Zhang <wenjia@...ux.ibm.com>,
 Mahanta Jambigi <mjambigi@...ux.ibm.com>, Tony Lu
 <tonylu@...ux.alibaba.com>, Wen Gu <guwen@...ux.alibaba.com>,
 netdev@...r.kernel.org, linux-doc@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-rdma@...r.kernel.org,
 linux-s390@...r.kernel.org
Subject: Re: [PATCH net-next v3 1/2] net/smc: make wr buffer count
 configurable

On 9/21/25 11:44 PM, Halil Pasic wrote:
> diff --git a/Documentation/networking/smc-sysctl.rst b/Documentation/networking/smc-sysctl.rst
> index a874d007f2db..c94d750c7c84 100644
> --- a/Documentation/networking/smc-sysctl.rst
> +++ b/Documentation/networking/smc-sysctl.rst
> @@ -71,3 +71,39 @@ smcr_max_conns_per_lgr - INTEGER
>  	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 a bottleneck in a sense that threads

missing 'be' or 'become'           here^^

> +	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 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 a bottleneck in a sense that threads

same                               here^^

[...]
> @@ -683,6 +678,8 @@ int smc_ib_create_queue_pair(struct smc_link *lnk)
>  	};
>  	int rc;
>  
> +	qp_attr.cap.max_send_wr = 3 * lnk->lgr->max_send_wr;
> +	qp_attr.cap.max_recv_wr = lnk->lgr->max_recv_wr;

Possibly:

	cap = max(3 * lnk->lgr->max_send_wr, lnk->lgr->max_recv_wr);
	qp_attr.cap.max_send_wr = cap;
	qp_attr.cap.max_recv_wr = cap

to avoid assumption on `max_send_wr`, `max_recv_wr` relative values.

[...]
> diff --git a/net/smc/smc_sysctl.h b/net/smc/smc_sysctl.h
> index eb2465ae1e15..8538915af7af 100644
> --- a/net/smc/smc_sysctl.h
> +++ b/net/smc/smc_sysctl.h
> @@ -25,6 +25,8 @@ static inline int smc_sysctl_net_init(struct net *net)
>  	net->smc.sysctl_autocorking_size = SMC_AUTOCORKING_DEFAULT_SIZE;
>  	net->smc.sysctl_max_links_per_lgr = SMC_LINKS_PER_LGR_MAX_PREFER;
>  	net->smc.sysctl_max_conns_per_lgr = SMC_CONN_PER_LGR_PREFER;
> +	net->smc.sysctl_smcr_max_send_wr = SMCR_MAX_SEND_WR_DEF;
> +	net->smc.sysctl_smcr_max_recv_wr = SMCR_MAX_RECV_WR_DEF;
>  	return 0;
>  }
>  
> diff --git a/net/smc/smc_wr.c b/net/smc/smc_wr.c
> index b04a21b8c511..f5b2772414fd 100644
> --- a/net/smc/smc_wr.c
> +++ b/net/smc/smc_wr.c
> @@ -34,6 +34,7 @@
>  #define SMC_WR_MAX_POLL_CQE 10	/* max. # of compl. queue elements in 1 poll */
>  
>  #define SMC_WR_RX_HASH_BITS 4
> +

Please avoid unrelated whitespace only changes.

Thanks,

Paolo