netdev - Re: [PATCH 20/21] net: warn if drivers set tx_queue

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Message-ID: <1440016319.6610.28.camel@edumazet-glaptop2.roam.corp.google.com>
Date:	Wed, 19 Aug 2015 13:31:59 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Phil Sutter <phil@....cc>
Cc:	netdev@...r.kernel.org, brouer@...hat.com, davem@...emloft.net
Subject: Re: [PATCH 20/21] net: warn if drivers set tx_queue_len = 0

On Wed, 2015-08-19 at 22:21 +0200, Phil Sutter wrote:
> On Wed, Aug 19, 2015 at 08:39:24PM +0200, Phil Sutter wrote:
> [...]
> > I'll start implementing the above immediately, but would appreciate to
> > hear your comments on it meanwhile. I wonder especially what makes the
> > difference between pfifo and pfifo_fast and why the latter can't be
> > selected explicitly by a user yet. Are there any good reasons for it
> > aside from it being the "default" and therefore selecting it can be done
> > by having tx_queue_len > 0 and removing the root qdisc?
> 
> Please ignore most of my questions regarding pfifo_fast here. I based my
> assumptions upon 'tc' utility of RHEL7, which is buggy in that it does
> not allow to add qdiscs which do not support extra options. Using
> mainline tc, pfifo_fast can be attached just like any other qdisc.
> 
> Sorry for the noise,

Yes, I was about to send you :

lpaa5:~# tc qd sh dev eth1
qdisc mq 0: root 
qdisc fq 0: parent :4 limit 10000p flow_limit 1000p buckets 1024 bands 3 priomap 1 2 2 2 1 2 0 0 1 1 1 1 1 1 1 1 quantum 3028 initial_quantum 15140 
qdisc fq 0: parent :3 limit 10000p flow_limit 1000p buckets 1024 bands 3 priomap 1 2 2 2 1 2 0 0 1 1 1 1 1 1 1 1 quantum 3028 initial_quantum 15140 
qdisc fq 0: parent :2 limit 10000p flow_limit 1000p buckets 1024 bands 3 priomap 1 2 2 2 1 2 0 0 1 1 1 1 1 1 1 1 quantum 3028 initial_quantum 15140 
qdisc fq 0: parent :1 limit 10000p flow_limit 1000p buckets 1024 bands 3 priomap 1 2 2 2 1 2 0 0 1 1 1 1 1 1 1 1 quantum 3028 initial_quantum 15140 
lpaa5:~# tc qd replace dev eth1 root pfifo_fast
lpaa5:~# tc -s -d qd sh dev eth1
qdisc pfifo_fast 8003: root refcnt 45 bands 3 priomap  1 2 2 2 1 2 0 0 1 1 1 1 1 1 1 1
 Sent 2662 bytes 22 pkt (dropped 0, overlimits 0 requeues 0) 
 backlog 0b 0p requeues 0 


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