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

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Date:	Mon, 24 Feb 2014 14:13:45 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Julian Anastasov <ja@....bg>
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

On Mon, 2014-02-24 at 22:47 +0200, Julian Anastasov wrote:
> 	Hello,
> 
> On Mon, 24 Feb 2014, Eric Dumazet wrote:
> 
> > v4: switch to ktime_get() instead of ktime_get_real()
> 
> 	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.

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 ?

Thanks !


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