netdev - Re: [PATCH net] macvlan: allow to enqueue broadcast pkt on virtual device

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Message-ID: <CAHA+R7M=Wp1u1hXD9YE52Ct74KOovEaVjCECV_5EsrAO_rJ7ag@mail.gmail.com>
Date:	Fri, 19 Sep 2014 14:59:29 -0700
From:	Cong Wang <cwang@...pensource.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Nicolas Dichtel <nicolas.dichtel@...nd.com>,
	David Miller <davem@...emloft.net>,
	netdev <netdev@...r.kernel.org>,
	Herbert Xu <herbert@...dor.apana.org.au>
Subject: Re: [PATCH net] macvlan: allow to enqueue broadcast pkt on virtual device

On Fri, Sep 19, 2014 at 2:35 PM, Eric Dumazet <eric.dumazet@...il.com> wrote:
> On Fri, 2014-09-19 at 14:24 -0700, Cong Wang wrote:
>> On Wed, Sep 17, 2014 at 1:08 AM, Nicolas Dichtel
>> <nicolas.dichtel@...nd.com> wrote:
>> > Since commit 412ca1550cbe ("macvlan: Move broadcasts into a work queue"), the
>> > driver uses tx_queue_len of the master device as the limit of packets enqueuing.
>> > Problem is that virtual drivers have this value set to 0, thus all broadcast
>> > packets were rejected.
>> > Because tx_queue_len was arbitrarily chosen, I replace it with a static limit
>> > of 1000 (also arbitrarily chosen).
>> >
>>
>> Hmm, why not manually set this tx_queue_len to fix it?
>>
>> At least fifo qdisc also uses tx_queue_len, and when you bond
>> you have to set it to non-zero.
>
>
> This is not true. We usually leave virtual devices with tx_queue_len to
> 0, otherwise you get a qdisc on them for nothing...

Yeah, actually it is 1 if tx_queue_len is 0, my memory mistaken.
But many virtual devices like veth call ether_setup() therefore have
tx_queue_len = 1000, not 0. dummy and bonding are 0 though.

>
> Only when you want to have say HTB on the bonding, you might need to
> change tx_queue_len

HTB by default creates a fifo qdisc.... same thing as above.

>
>>
>> I am not saying using this tx_queue_len is absolutely correct,
>> I am saying it may be expected to set tx_queue_len by yourself.
>
> I disagree.
>

Then fix these tx_queue_len = 0?
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