netdev - Re: [PATCH net-next 3/4] tcp: add SACK compression

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Date:   Thu, 17 May 2018 08:46:26 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Neal Cardwell <ncardwell@...gle.com>,
        Eric Dumazet <edumazet@...gle.com>
Cc:     David Miller <davem@...emloft.net>,
        Netdev <netdev@...r.kernel.org>,
        Toke Høiland-Jørgensen <toke@...e.dk>,
        Yuchung Cheng <ycheng@...gle.com>,
        Soheil Hassas Yeganeh <soheil@...gle.com>
Subject: Re: [PATCH net-next 3/4] tcp: add SACK compression



On 05/17/2018 08:40 AM, Eric Dumazet wrote:
> 
> 
> On 05/17/2018 08:14 AM, Neal Cardwell wrote:

>> Any particular motivation for the 2.5ms here? It might be nice to match the
>> existing TSO autosizing dynamics and use 1ms here instead of having a
>> separate new constant of 2.5ms. Smaller time scales here should lead to
>> less burstiness and queue pressure from data packets in the network, and we
>> know from experience that the CPU overhead of 1ms chunks is acceptable.
> 
> This came from my tests on wifi really :)
> 
> I also had the idea to make this threshold adjustable for wifi, like we did for sk_pacing_shift.
> 
> (On wifi, we might want to increase the max delay between ACK)
> 
> So maybe use 1ms delay, when sk_pacing_shift == 10, but increase it if sk_pacing_shift has been lowered.
> 
>

BTW, maybe my changelog or patch is not clear enough :

As soon as some packets are received in order, we send an ACK, even if the timer was armed.
(This is the beginning of __tcp_ack_snd_check())

When this ACK is sent, timer is canceled (in tcp_event_ack_sent())