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

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Message-ID: <CAB_+Fg6O8bsuromuPns8G3q+LSV-bqvJL11H6GoJGEpqhyrU=w@mail.gmail.com>
Date:	Fri, 19 Aug 2011 00:34:34 -0700
From:	Nandita Dukkipati <nanditad@...gle.com>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	"David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org,
	Tom Herbert <therbert@...gle.com>,
	Yuchung Cheng <ycheng@...gle.com>,
	Matt Mathis <mattmathis@...gle.com>
Subject: Re: [PATCH] Proportional Rate Reduction for TCP.

On Sat, Aug 13, 2011 at 10:05 PM, Andi Kleen <andi@...stfloor.org> wrote:
> Nandita Dukkipati <nanditad@...gle.com> writes:
>> +
>> +     if (tcp_packets_in_flight(tp) > tp->snd_ssthresh) {
>> +             if (WARN_ON(!tp->prr_cwnd))
>> +                     tp->prr_cwnd = 1;
>> +             sndcnt = DIV_ROUND_UP(tp->prr_delivered * tp->snd_ssthresh,
>> +                                   tp->prr_cwnd) - tp->prr_out;
>> +     } else {
>> +             sndcnt = min_t(int, delta,
>> +                            max_t(int, tp->prr_delivered -
>> tp->prr_out,
>
> u32s here? This will likely do bad things with large enough windows.

Fixed in patch v2.

>
> The rest looks good to me as code, but I don't claim to fully understand the
> algorithm. Perhaps a sysctl to turn it off and a linux mib counter when
> it triggers would be useful in addition.

There already exists a mib counter when entering Recovery state, so
this will be incremented when PRR is triggered.

Thanks
Nandita
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