netdev - Re: [PATCH v2 net-next] pkt_sched: fq: Fair Queue packet scheduler

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Message-ID: <1378344185.11205.3.camel@edumazet-glaptop>
Date:	Wed, 04 Sep 2013 18:23:05 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Jason Wang <jasowang@...hat.com>
Cc:	David Miller <davem@...emloft.net>,
	netdev <netdev@...r.kernel.org>,
	Yuchung Cheng <ycheng@...gle.com>,
	Neal Cardwell <ncardwell@...gle.com>,
	"Michael S. Tsirkin" <mst@...hat.com>
Subject: Re: [PATCH v2 net-next] pkt_sched: fq: Fair Queue packet scheduler

On Wed, 2013-09-04 at 17:50 -0700, Eric Dumazet wrote:

> 
> BTW what is your HZ value ?
> 
> We have a problem in TCP stack, because srtt is in HZ units.
> 
> Before we change to us units, I guess tcp_update_pacing_rate() should be
> changed a bit if HZ=250

Oh well, I feel dumb, please try this fix (If you have HZ != 1000) :

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 93d7e9d..fd96d8e 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -700,7 +700,7 @@ static void tcp_update_pacing_rate(struct sock *sk)
 	u64 rate;
 
 	/* set sk_pacing_rate to 200 % of current rate (mss * cwnd / srtt) */
-	rate = (u64)tp->mss_cache * 2 * (HZ << 3);
+	rate = (u64)tp->mss_cache * 2 * ((USEC_PER_SEC/HZ) << 3);
 
 	rate *= max(tp->snd_cwnd, tp->packets_out);
 


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