netdev - Re: [PATCH net 1/4] Revert "net/smc: don't wait for send buffer space when data was already sent"

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Date:   Wed, 27 Oct 2021 12:21:32 +0200
From:   Karsten Graul <kgraul@...ux.ibm.com>
To:     Tony Lu <tonylu@...ux.alibaba.com>, davem@...emloft.net,
        kuba@...nel.org
Cc:     netdev@...r.kernel.org, linux-s390@...r.kernel.org,
        linux-rdma@...r.kernel.org, jacob.qi@...ux.alibaba.com,
        xuanzhuo@...ux.alibaba.com, guwen@...ux.alibaba.com,
        dust.li@...ux.alibaba.com
Subject: Re: [PATCH net 1/4] Revert "net/smc: don't wait for send buffer space
 when data was already sent"

On 27/10/2021 10:52, Tony Lu wrote:
> From: Tony Lu <tony.ly@...ux.alibaba.com>
> 
> This reverts commit 6889b36da78a21a312d8b462c1fa25a03c2ff192.
> 
> When using SMC to replace TCP, some userspace applications like netperf
> don't check the return code of send syscall correctly, which means how
> many bytes are sent. If rc of send() is smaller than expected, it should
> try to send again, instead of exit directly. It is difficult to change
> the uncorrect behaviors of userspace applications, so choose to revert it.

Your change would restore the old behavior to handle all sockets like they 
are blocking sockets, trying forever to send the provided data bytes.
This is not how it should work.

We encountered the same issue with netperf, but this is the only 'broken'
application that we know of so far which does not implement the socket API
correctly.