netdev - Re: [PATCH net-next] tcp/fq: move back to CLOCK

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Message-Id: <20181001.231920.987040554483569743.davem@davemloft.net>
Date:   Mon, 01 Oct 2018 23:19:20 -0700 (PDT)
From:   David Miller <davem@...emloft.net>
To:     edumazet@...gle.com
Cc:     netdev@...r.kernel.org, eric.dumazet@...il.com,
        leonard.crestez@....com
Subject: Re: [PATCH net-next] tcp/fq: move back to CLOCK_MONOTONIC

From: Eric Dumazet <edumazet@...gle.com>
Date: Fri, 28 Sep 2018 10:28:44 -0700

> In the recent TCP/EDT patch series, I switched TCP and sch_fq
> clocks from MONOTONIC to TAI, in order to meet the choice done
> earlier for sch_etf packet scheduler.
> 
> But sure enough, this broke some setups were the TAI clock
> jumps forward (by almost 50 year...), as reported
> by Leonard Crestez.
> 
> If we want to converge later, we'll probably need to add
> an skb field to differentiate the clock bases, or a socket option.
> 
> In the meantime, an UDP application will need to use CLOCK_MONOTONIC
> base for its SCM_TXTIME timestamps if using fq packet scheduler.
> 
> Fixes: 72b0094f9182 ("tcp: switch tcp_clock_ns() to CLOCK_TAI base")
> Fixes: 142537e41923 ("net_sched: sch_fq: switch to CLOCK_TAI")
> Fixes: fd2bca2aa789 ("tcp: switch internal pacing timer to CLOCK_TAI")
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> Reported-by: Leonard Crestez <leonard.crestez@....com>

Applied.