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

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Date:	Fri, 19 Aug 2011 13:25:24 +0300 (EEST)
From:	"Ilpo Järvinen" <ilpo.jarvinen@...sinki.fi>
To:	Nandita Dukkipati <nanditad@...gle.com>
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.

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.

> +		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).

-- 
 i.
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