netdev - Re: [PATCH net] tcp: lack of available data can also cause TSO defer

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Date:   Fri, 07 Dec 2018 16:18:59 -0800 (PST)
From:   David Miller <davem@...emloft.net>
To:     edumazet@...gle.com
Cc:     netdev@...r.kernel.org, ncardwell@...gle.com, soheil@...gle.com,
        ycheng@...gle.com, eric.dumazet@...il.com
Subject: Re: [PATCH net] tcp: lack of available data can also cause TSO
 defer

From: Eric Dumazet <edumazet@...gle.com>
Date: Thu,  6 Dec 2018 09:58:24 -0800

> tcp_tso_should_defer() can return true in three different cases :
> 
>  1) We are cwnd-limited
>  2) We are rwnd-limited
>  3) We are application limited.
> 
> Neal pointed out that my recent fix went too far, since
> it assumed that if we were not in 1) case, we must be rwnd-limited
> 
> Fix this by properly populating the is_cwnd_limited and
> is_rwnd_limited booleans.
> 
> After this change, we can finally move the silly check for FIN
> flag only for the application-limited case.
> 
> The same move for EOR bit will be handled in net-next,
> since commit 1c09f7d073b1 ("tcp: do not try to defer skbs
> with eor mark (MSG_EOR)") is scheduled for linux-4.21
> 
> Tested by running 200 concurrent netperf -t TCP_RR -- -r 60000,100
> and checking none of them was rwnd_limited in the chrono_stat
> output from "ss -ti" command.
> 
> Fixes: 41727549de3e ("tcp: Do not underestimate rwnd_limited")
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> Suggested-by: Neal Cardwell <ncardwell@...gle.com>
> Reviewed-by: Neal Cardwell <ncardwell@...gle.com>
> Acked-by: Soheil Hassas Yeganeh <soheil@...gle.com>
> Reviewed-by: Yuchung Cheng <ycheng@...gle.com>

Applied.