netdev - Re: [PATCH v2] Proportional Rate Reduction for TCP.

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Date:	Fri, 19 Aug 2011 18:28:58 -0700
From:	Nandita Dukkipati <nanditad@...gle.com>
To:	Ilpo Järvinen <ilpo.jarvinen@...sinki.fi>
Cc:	"David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org,
	Tom Herbert <therbert@...gle.com>,
	Matt Mathis <mattmathis@...gle.com>,
	Yuchung Cheng <ycheng@...gle.com>
Subject: Re: [PATCH v2] Proportional Rate Reduction for TCP.

Forgot to turn off gmail's rich formatting, so re-sending to the list.

On Fri, Aug 19, 2011 at 3:25 AM, Ilpo Järvinen
<ilpo.jarvinen@...sinki.fi> wrote:
>
> On Fri, 19 Aug 2011, Nandita Dukkipati wrote:
>
> > +static void tcp_update_cwnd_in_recovery(struct sock *sk, int newly_acked_sacked,
> > +                                     int fast_rexmit, int flag)
> > +{
> > +     struct tcp_sock *tp = tcp_sk(sk);
> > +     int sndcnt = 0;
> > +     int delta = tp->snd_ssthresh - tcp_packets_in_flight(tp);
> > +
> > +     if (tcp_packets_in_flight(tp) > tp->snd_ssthresh) {
> > +             if (WARN_ON(!tp->prior_cwnd))
> > +                     tp->prior_cwnd = 1;
>
> This should still be made larger to avoid problems if it ever will be
> needed.

I am letting the value remain at 1, mainly because this is the valid
lowest non-zero value for snd_cwnd to take on. The main purpose of
this code is to catch any lurking bug outside of PRR which results in
an undesirable divide by 0 in PRR. I would like to fix that bug if I
find this code is executed.

>
> > +             sndcnt = DIV_ROUND_UP((u64)(tp->prr_delivered *
> > +                                         tp->snd_ssthresh),
> > +                                   (u64)tp->prior_cwnd) - tp->prr_out;
>
> I think you should pick one from include/linux/math64.h instead of letting
> gcc to do / operand all by itself. ...Obviosly then the ROUND_UP part
> needs to be done manually (either using the remainder or pre-addition
> like DIV_ROUND_UP does).

Done. patch v3 used div_u64.

Thanks
Nandita
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