netdev - Re: [PATCH net] sctp: not allow to set rto

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Message-ID: <20180529170604.GD3788@localhost.localdomain>
Date:   Tue, 29 May 2018 14:06:04 -0300
From:   Marcelo Ricardo Leitner <marcelo.leitner@...il.com>
To:     Neal Cardwell <ncardwell@...gle.com>
Cc:     Michael Tuexen <michael.tuexen@...chi.franken.de>,
        nhorman@...driver.com, Dmitry Vyukov <dvyukov@...gle.com>,
        lucien.xin@...il.com, Netdev <netdev@...r.kernel.org>,
        linux-sctp@...r.kernel.org, David Miller <davem@...emloft.net>,
        dsa@...ulusnetworks.com, Eric Dumazet <edumazet@...gle.com>,
        syzkaller@...glegroups.com
Subject: Re: [PATCH net] sctp: not allow to set rto_min with a value below
 200 msecs

On Tue, May 29, 2018 at 12:03:46PM -0400, Neal Cardwell wrote:
> On Tue, May 29, 2018 at 11:45 AM Marcelo Ricardo Leitner <
> marcelo.leitner@...il.com> wrote:
> > - patch2 - fix rtx attack vector
> >    - Add the floor value to rto_min to HZ/20 (which fits the values
> >      that Michael shared on the other email)
> 
> I would encourage allowing minimum RTO values down to 5ms, if the ACK
> policy in the receiver makes this feasible. Our experience is that in
> datacenter environments it can be advantageous to allow timer-based loss
> recoveries using timeout values as low as 5ms, e.g.:

Thanks Neal. On Xin's tests, the hearbeat timer becomes an issue at
~25ms already. Xin, can you share more details on the hw, which CPU
was used?

Anyway, what about we add a floor to rto_max too, so that RTO can
actually grow into something bigger that don't hog the CPU? Like:
rto_min floor = 5ms
rto_max floor = 50ms

  Marcelo