netdev - Re: [PATCH v2] tcp: adjust rcvbuff according copied rate of user space

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Date:   Thu, 11 Aug 2022 16:14:49 +0800
From:   Yonglong Li <liyonglong@...natelecom.cn>
To:     Neal Cardwell <ncardwell@...gle.com>
Cc:     netdev@...r.kernel.org, davem@...emloft.net, edumazet@...gle.com,
        ycheng@...gle.com, dsahern@...nel.org, kuba@...nel.org,
        pabeni@...hat.com
Subject: Re: [PATCH v2] tcp: adjust rcvbuff according copied rate of user
 space



On 8/10/2022 8:43 PM, Neal Cardwell wrote:
> On Wed, Aug 10, 2022 at 3:49 AM Yonglong Li <liyonglong@...natelecom.cn> wrote:
>>
>> every time data is copied to user space tcp_rcv_space_adjust is called.
>> current It adjust rcvbuff by the length of data copied to user space.
>> If the interval of user space copy data from socket is not stable, the
>> length of data copied to user space will not exactly show the speed of
>> copying data from rcvbuff.
>> so in tcp_rcv_space_adjust it is more reasonable to adjust rcvbuff by
>> copied rate (length of copied data/interval)instead of copied data len
>>
>> I tested this patch in simulation environment by Mininet:
>> with 80~120ms RTT / 1% loss link, 100 runs
>> of (netperf -t TCP_STREAM -l 5), and got an average throughput
>> of 17715 Kbit instead of 17703 Kbit.
>> with 80~120ms RTT without loss link, 100 runs of (netperf -t
>> TCP_STREAM -l 5), and got an average throughput of 18272 Kbit
>> instead of 18248 Kbit.
> 
> So with 1% emulated loss that's a 0.06% throughput improvement and
> without emulated loss that's a 0.13% improvement. That sounds like it
> may well be statistical noise, particularly given that we would expect
> the steady-state impact of this change to be negligible.
> 
Hi neal,

Thank you for your feedback.
I don't think the improvement is statistical noise. Because I can get small
improvement after patch every time I test.


-- 
Li YongLong