netdev - Re: [PATCH net-next] tcp: fix TCP

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Message-ID: <CACSApvbxXWq3VJzGxxjOeqtpsF9=Hkn+MOrqGRqbzk7FeX8_tg@mail.gmail.com>
Date:   Tue, 23 May 2017 15:47:02 -0400
From:   Soheil Hassas Yeganeh <soheil@...gle.com>
To:     Eric Dumazet <eric.dumazet@...il.com>
Cc:     David Miller <davem@...emloft.net>,
        netdev <netdev@...r.kernel.org>,
        Yuchung Cheng <ycheng@...gle.com>
Subject: Re: [PATCH net-next] tcp: fix TCP_SYNCNT flakes

On Tue, May 23, 2017 at 3:38 PM, Eric Dumazet <eric.dumazet@...il.com> wrote:
> From: Eric Dumazet <edumazet@...gle.com>
>
> After the mentioned commit, some of our packetdrill tests became flaky.
>
> TCP_SYNCNT socket option can limit the number of SYN retransmits.
>
> retransmits_timed_out() has to compare times computations based on
> local_clock() while timers are based on jiffies. With NTP adjustments
> and roundings we can observe 999 ms delay for 1000 ms timers.
> We end up sending one extra SYN packet.
>
> Gimmick added in commit 6fa12c850314 ("Revert Backoff [v3]: Calculate
> TCP's connection close threshold as a time value") makes no
> real sense for TCP_SYN_SENT sockets where no RTO backoff can happen at
> all.
>
> Lets use a simpler logic for TCP_SYN_SENT sockets and remove @syn_set
> parameter from retransmits_timed_out()
>
> Fixes: 9a568de4818d ("tcp: switch TCP TS option (RFC 7323) to 1ms clock")
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> Signed-off-by: Yuchung Cheng <ycheng@...gle.com>

Acked-by: Soheil Hassas Yeganeh <soheil@...gle.com>

Nice!