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

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Message-ID: <20250925132540.74091295.pasic@linux.ibm.com>
Date: Thu, 25 Sep 2025 13:25:40 +0200
From: Halil Pasic <pasic@...ux.ibm.com>
To: Paolo Abeni <pabeni@...hat.com>
Cc: 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, Halil Pasic <pasic@...ux.ibm.com>
Subject: Re: [PATCH net-next v3 1/2] net/smc: make wr buffer count
 configurable

On Thu, 25 Sep 2025 11:27:38 +0200
Paolo Abeni <pabeni@...hat.com> wrote:
[..]
> > +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^^

Sorry about those! Will fix for v4.

> 
> [...]
> > @@ -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.

Can you explain a little more. I'm happy to do the change, but I would
prefer to understand why is keeping qp_attr.cap.max_send_wr ==
qp_attr.cap.max_recv_wr better? But if you tell: "Just trust me!" I will.

[..]

> >  
> > 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.

Will fix  for v4. Really sorry!

Regards,
Halil