netdev - Re: [net-next PATCH 1/3] net: make default tx_queue

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Message-ID: <1439391326.29802.12.camel@edumazet-glaptop2.roam.corp.google.com>
Date:	Wed, 12 Aug 2015 07:55:26 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc:	Jesper Dangaard Brouer <brouer@...hat.com>,
	David Miller <davem@...emloft.net>, fw@...len.de,
	netdev@...r.kernel.org, cwang@...pensource.com
Subject: Re: [net-next PATCH 1/3] net: make default tx_queue_len configurable

On Tue, 2015-08-11 at 18:13 -0700, Alexei Starovoitov wrote:
> Also why introduce the flag? Why not just add 'tx_queue_len = 0;' 
> to veth_setup() like the whole bunch of devices do?

Sigh.

Because some people install htb or pfifo on veth, leaving tx_queue_len
unchanged.

If you install htb while tx_queue_len is 0, pfifo created on htb classe
can only queue one packet.


static int fifo_init(struct Qdisc *sch, struct nlattr *opt)
{
        bool bypass;
        bool is_bfifo = sch->ops == &bfifo_qdisc_ops;

        if (opt == NULL) {
                u32 limit = qdisc_dev(sch)->tx_queue_len ? : 1;

                if (is_bfifo)
                        limit *= psched_mtu(qdisc_dev(sch));

                sch->limit = limit;



Changing veth txqueuelen is too late.


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