netdev - Re: [PATCH v4 net-next] tcp: switch rtt estimations to usec resolution

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Date:	Tue, 25 Feb 2014 01:01:18 +0200 (EET)
From:	Julian Anastasov <ja@....bg>
To:	Eric Dumazet <eric.dumazet@...il.com>
cc:	David Miller <davem@...emloft.net>,
	Yuchung Cheng <ycheng@...gle.com>,
	netdev <netdev@...r.kernel.org>,
	Neal Cardwell <ncardwell@...gle.com>,
	Larry Brakmo <brakmo@...gle.com>
Subject: Re: [PATCH v4 net-next] tcp: switch rtt estimations to usec
 resolution


	Hello,

On Mon, 24 Feb 2014, Eric Dumazet wrote:

> On Mon, 2014-02-24 at 22:47 +0200, Julian Anastasov wrote:
> > 
> > 	May be you missed my last email. In tcpm_suck_dst()
> > dst_metric_raw(dst, RTAX_RTT) returns msecs and we store
> > it in tcpm_vals[] which is now in usec units. If we want to keep
> > dst metrics in msec units we can fix this only in tcpm_suck_dst.
> > Otherwise, similar attributes for dst metrics in ip/iproute.c
> > are needed.
> 
> Well, I do not see an immediate need to support usec for these
> attributes. This might be changed later if needed.

	Agreed.

> So I think we can simply do :
> 
> 
> diff --git a/net/ipv4/tcp_metrics.c b/net/ipv4/tcp_metrics.c
> index d547075d8300..c8d0b1b18b8e 100644
> --- a/net/ipv4/tcp_metrics.c
> +++ b/net/ipv4/tcp_metrics.c
> -static void tcpm_suck_dst(struct tcp_metrics_block *tm, struct dst_entry *dst,
> +static void tcpm_suck_dst(struct tcp_metrics_block *tm,
> +                         const struct dst_entry *dst,
>                           bool fastopen_clear)
>  {
> +       u32 msval;
>         u32 val;
>  
>         tm->tcpm_stamp = jiffies;
> @@ -121,8 +115,11 @@ static void tcpm_suck_dst(struct tcp_metrics_block *tm, struct dst_entry *dst,
>                 val |= 1 << TCP_METRIC_REORDERING;
>         tm->tcpm_lock = val;
>  
> -       tm->tcpm_vals[TCP_METRIC_RTT] = dst_metric_raw(dst, RTAX_RTT);
> -       tm->tcpm_vals[TCP_METRIC_RTTVAR] = dst_metric_raw(dst, RTAX_RTTVAR);
> +       msval = dst_metric_raw(dst, RTAX_RTT);
> +       tm->tcpm_vals[TCP_METRIC_RTT] = msval * USEC_PER_MSEC;
> +
> +       msval = dst_metric_raw(dst, RTAX_RTTVAR);
> +       tm->tcpm_vals[TCP_METRIC_RTTVAR] = msval * USEC_PER_MSEC;
>         tm->tcpm_vals[TCP_METRIC_SSTHRESH] = dst_metric_raw(dst, RTAX_SSTHRESH);
>         tm->tcpm_vals[TCP_METRIC_CWND] = dst_metric_raw(dst, RTAX_CWND);
>         tm->tcpm_vals[TCP_METRIC_REORDERING] = dst_metric_raw(dst, RTAX_REORDERING);
> 
> Is that ok ?

	Yes, looks fine. Thanks!

Regards

--
Julian Anastasov <ja@....bg>
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