netdev - Re: [PATCH 4/7] tcp_cubic: fix clock dependency

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Date:	Mon, 14 Mar 2011 14:21:25 -0700
From:	Stephen Hemminger <shemminger@...tta.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	"David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org
Subject: Re: [PATCH 4/7] tcp_cubic: fix clock dependency

On Mon, 14 Mar 2011 19:51:19 +0100
Eric Dumazet <eric.dumazet@...il.com> wrote:

> Le lundi 14 mars 2011 à 10:52 -0700, Stephen Hemminger a écrit :
> > pièce jointe document texte brut (tcp-cubic-minrtt.patch)
> > The hystart code was written with assumption that HZ=1000.
> > Replace the use of jiffies with bictcp_clock as a millisecond
> > real time clock. 
> > 
> > Signed-off-by: Stephen Hemminger <shemminger@...tta.com>
> > Reported-by: Lucas Nussbaum <lucas.nussbaum@...ia.fr>
> > 
> > --- a/net/ipv4/tcp_cubic.c	2011-03-14 08:19:18.000000000 -0700
> > +++ b/net/ipv4/tcp_cubic.c	2011-03-14 08:22:42.486690594 -0700
> > @@ -88,7 +88,7 @@ struct bictcp {
> >  	u32	last_time;	/* time when updated last_cwnd */
> >  	u32	bic_origin_point;/* origin point of bic function */
> >  	u32	bic_K;		/* time to origin point from the beginning of the current epoch */
> > -	u32	delay_min;	/* min delay */
> > +	u32	delay_min;	/* min delay (msec << 3) */
> >  	u32	epoch_start;	/* beginning of an epoch */
> >  	u32	ack_cnt;	/* number of acks */
> >  	u32	tcp_cwnd;	/* estimated tcp cwnd */
> > @@ -98,7 +98,7 @@ struct bictcp {
> >  	u8	found;		/* the exit point is found? */
> >  	u32	round_start;	/* beginning of each round */
> >  	u32	end_seq;	/* end_seq of the round */
> > -	u32	last_jiffies;	/* last time when the ACK spacing is close */
> > +	u32	last_ack;	/* last time when the ACK spacing is close */
> >  	u32	curr_rtt;	/* the minimum rtt of current round */
> >  };
> >  
> > @@ -119,12 +119,21 @@ static inline void bictcp_reset(struct b
> >  	ca->found = 0;
> >  }
> >  
> > +static inline u32 bictcp_clock(void)
> > +{
> > +#if HZ < 1000
> > +	return ktime_to_ms(ktime_get_real());
> 
> Small point : This can be changed if date/time is changed
> 
> Maybe use monotonic time (aka ktime_get_ts()) ?

I choose get_real() because that is what skb timestamp is using;
both should probably use monotonic clock.


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