netdev - Re: [PATCH net-next v2] net/smc: Reduce overflow of smc clcsock listen queue

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Message-ID: <20220105150612.GA75522@e02h04389.eu6sqa>
Date:   Wed, 5 Jan 2022 23:06:12 +0800
From:   "D. Wythe" <alibuda@...ux.alibaba.com>
To:     Karsten Graul <kgraul@...ux.ibm.com>
Cc:     dust.li@...ux.alibaba.com, kuba@...nel.org, davem@...emloft.net,
        netdev@...r.kernel.org, linux-s390@...r.kernel.org,
        linux-rdma@...r.kernel.org
Subject: Re: [PATCH net-next v2] net/smc: Reduce overflow of smc clcsock
 listen queue

LGTM. Fallback makes the restrictions on SMC dangling
connections more meaningful to me, compared to dropping them.

Overall, i see there are two scenario.

1. Drop the overflow connections limited by userspace application
accept.

2. Fallback the overflow connections limited by the heavy process of
current SMC handshake. ( We can also control its behavior through
sysctl.)

I'll follow those advise to improve my patch, more advise will be highly
appreciated.

Thanks all. 


On Wed, Jan 05, 2022 at 02:17:41PM +0100, Karsten Graul wrote:
> On 05/01/2022 09:57, dust.li wrote:
> > On Wed, Jan 05, 2022 at 12:40:49PM +0800, D. Wythe wrote:
> > I'm thinking maybe we can actively fall back to TCP in this case ? Not
> > sure if this is a good idea.
> 
> I think its a good decision to switch new connections to use the TCP fallback when the
> current queue of connections waiting for a SMC handshake is too large.
> With this the application is able to accept all incoming connections and they are not
> dropped. The only thing that is be different compared to TCP is that the order of the
> accepted connections is changed, connections that came in later might reach the user space 
> application earlier than connections that still run the SMC hand shake processing. 
> But I think that is semantically okay.