Subject: Re: [PATCH net] sctp: not allow to set rto_min with a value below 200 msecs

From: Marcelo Ricardo Leitner <[email-masked]>
Date: Tue, 29 May 2018 14:06:04 -0300

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 <
> [email-masked]> 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