Re: [PATCH v3] mptcp: ensure there is unacked data at all subflow

[Yonglong Li <liyonglong@chinatelecom.cn>]

Hi Paolo,

Thanks for your feeback.

On 2021/4/1 18:08, Paolo Abeni wrote:
> Hello,
> 
> I'm sorry for the late feeback.
> 
> On Thu, 2021-04-01 at 15:53 +0800, Yonglong Li wrote:
>> MPTCP-level retransmit may take place if first subflow without data in
>> its write queue and second subflow is likely to have unacked data left
>> in its write queue. In this condition datamaybe double retransmitted.
> 
> Note that the above does not cause problems at the byte stream level,
> and can improve the aggregate tput in some cases, as it could allow
> faster forward progress when e.g. the substream which originally
> handled the relevant data has experienced some congestion.
> 
> Do you have any specific scenario which is badly affected by the
> current code? How does the self-tests behave on top of this patch?
> (specifically: simult_flows.sh)

In my test, current code doesn't cause any badly affected. And in some
cases it can improve the tput in theory (re-injection likely). But the
behave of current code is not stable. In some cases it 're-injection'
data, and some cases it does not. And as you said at "Side note" the
're-injection' should not do at mptcp_subflow_get_retrans()

> 
> Side note: we could improve re-injection keeping explicit track at the
>  mptcp_data_frag level of the already used subflows, and avoding them
> at mptcp_subflow_get_retrans() time.
> 
> Thanks!
> 
> Paolo
> 
> 
>