netdev - Re: [PATCH net-next] fq_codel: report congestion notification at enqueue time

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Message-ID: <1340949008.29822.73.camel@edumazet-glaptop>
Date:	Fri, 29 Jun 2012 07:50:08 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	David Miller <davem@...emloft.net>
Cc:	netdev@...r.kernel.org, dave.taht@...il.com,
	codel@...ts.bufferbloat.net, therbert@...gle.com,
	mattmathis@...gle.com, ycheng@...gle.com, nanditad@...gle.com,
	ncardwell@...gle.com
Subject: Re: [PATCH net-next] fq_codel: report congestion notification at
 enqueue time

On Thu, 2012-06-28 at 22:29 -0700, David Miller wrote:

> I am pretty sure the behavior in RED is intentional.
> 
> It's a soft push back on TCP.
> 

tcp_enter_cwr() is called the same for DROP and CN

> We're taking this path when we are unable to sucessfully ECN mark a
> packet.  But our intention was to do so.
> 

Hmm, problem is the sender thinks the packet was queued for
transmission.

        ret = macvlan_queue_xmit(skb, dev);
        if (likely(ret == NET_XMIT_SUCCESS || ret == NET_XMIT_CN)) {
                struct macvlan_pcpu_stats *pcpu_stats;

                pcpu_stats = this_cpu_ptr(vlan->pcpu_stats);
                u64_stats_update_begin(&pcpu_stats->syncp);
                pcpu_stats->tx_packets++;
                pcpu_stats->tx_bytes += len;
                u64_stats_update_end(&pcpu_stats->syncp);
        } else {
                this_cpu_inc(vlan->pcpu_stats->tx_dropped);
        }

NET_XMIT_CN has a lazy semantic it seems.

I will just dont rely on it.



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