netdev - Re: Packet loss when txqueuelen is zero

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Date:	Sun, 29 Jun 2014 15:51:33 +0200
From:	Stefan Wahren <info@...egoodbye.de>
To:	Eric Dumazet <eric.dumazet@...il.com>
CC:	netdev@...r.kernel.org, arnd@...db.de
Subject: Re: Packet loss when txqueuelen is zero

Am 28.06.2014 16:40, schrieb Eric Dumazet:
>>
>> Is the packet loss a expected result for this scenario?
>
> Sure it is totally expected.
>
> -f is a flood ping, and you remove ability to store packets in the Qdisc
> (pifo_fast limit is device txqueuelen).
>
> If you have txqueuelen = 100, then the socket used by ping will more
> likely hit its SO_SNDBUF limit and ping will handle this properly (it
> detects that a sendmsg() returns -1, errno = ENOBUF
>
> If QCA7000 network driver has a tx ring size of 10 packets, you really
> want a qdisc being able to store bursts.

Thanks for your explanation. So it's not a network driver bug.

>
> If bufferbloat is your concern, you can switch pfifo_fast to fq_codel or
> fq
>
> tc qdisc replace dev eth0 root fq_codel  (or fq to get TCP pacing)
>

But fq_codel requires BQL in the QCA7000 network driver. Right?

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