netdev - Re: [PATCH net-next] tcp: Add tracepoint for rxtstamp coalescing

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Date: Fri, 14 Jun 2024 19:27:37 +0800
From: Philo Lu <lulie@...ux.alibaba.com>
To: Paolo Abeni <pabeni@...hat.com>, netdev@...r.kernel.org,
 edumazet@...gle.com
Cc: rostedt@...dmis.org, mhiramat@...nel.org, mathieu.desnoyers@...icios.com,
 davem@...emloft.net, dsahern@...nel.org, kuba@...nel.org,
 xuanzhuo@...ux.alibaba.com, dust.li@...ux.alibaba.com
Subject: Re: [PATCH net-next] tcp: Add tracepoint for rxtstamp coalescing



On 2024/6/14 16:09, Paolo Abeni wrote:
> On Tue, 2024-06-11 at 12:58 +0800, Philo Lu wrote:
>> During tcp coalescence, rx timestamps of the former skb ("to" in
>> tcp_try_coalesce), will be lost. This may lead to inaccurate
>> timestamping results if skbs come out of order.
>>
>> Here is an example.
>> Assume a message consists of 3 skbs, namely A, B, and C. And these skbs
>> are processed by tcp in the following order:
>> A -(1us)-> C -(1ms)-> B
> 
> IMHO the above order makes the changelog confusing
>
Thank you for pointing out this, I'll try to explain it in another way.

Here it means these packets come in order of A-C-B, and B comes much 
later than C, such as 1ms later. Currently, the 1ms delay would be lost 
because of tcp coalescing.

-- 
Philo