linux-kernel - Re: [PATCH net-next v5 1/2] net/smc: make wr buffer count configurable

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Message-ID: <aN0Cpw7mTtLdnBMZ@archie.me>
Date: Wed, 1 Oct 2025 17:29:59 +0700
From: Bagas Sanjaya <bagasdotme@...il.com>
To: Halil Pasic <pasic@...ux.ibm.com>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Simon Horman <horms@...nel.org>, Jonathan Corbet <corbet@....net>,
	"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>,
	Guangguan Wang <guangguan.wang@...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 v5 1/2] net/smc: make wr buffer count
 configurable

On Mon, Sep 29, 2025 at 02:00:00AM +0200, Halil Pasic wrote:
> diff --git a/Documentation/networking/smc-sysctl.rst b/Documentation/networking/smc-sysctl.rst
> index a874d007f2db..5de4893ef3e7 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
        So-called
> +	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 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
Ditto.
> +	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 give up much
> +	like before having this control.
> +
> +	Default: 48

Thanks.

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