lkml.org 
[lkml]   [2016]   [Feb]   [17]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
Date
From
SubjectRe: [PATCH] Revert "net: sched: drop all special handling of tx_queue_len == 0"
Hi,

On Tue, Feb 16, 2016 at 07:56:23PM -0500, Mathieu Desnoyers wrote:
> This reverts commit 348e3435cbefa815bd56a5205c1412b5afe7b92e.
> It breaks HTB classful qdiscs on the loopback interface.
>
> It has been broken since kernel v4.2. The offending commit has
> been identified by bissection of the issue with the following
> test-case. It appears that the loopback interface does indeed
> still have tx_queue_len == 0.
>
> Reverting the commit on a v4.4.1 kernel fixes the issue.

Indeed, this is ugly. Affected are all drivers not calling ether_setup()
in their setup callback, and therefore not initializing tx_queue_len.

As the commit to be reverted shows, there is no common fallback value
for tx_queue_len - most qdisc implementations used 1, but HTB fell back
to 2 and PLUG to 100. But as the removed comment in sch_plug.c stated:

| /* We will set a default limit of 100 pkts (~150kB)
| * in case tx_queue_len is not available. The
| * default value is completely arbitrary.
| */

It seems not to be overly important to fallback to the exact value each
qdisc had before. Therefore I guess the following change should
appropriately fix the issue at hand:

--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -7440,8 +7440,10 @@ struct net_device *alloc_netdev_mqs(int sizeof_priv, const char *name,
dev->priv_flags = IFF_XMIT_DST_RELEASE | IFF_XMIT_DST_RELEASE_PERM;
setup(dev);

- if (!dev->tx_queue_len)
+ if (!dev->tx_queue_len) {
dev->priv_flags |= IFF_NO_QUEUE;
+ dev->tx_queue_len = 1;
+ }

dev->num_tx_queues = txqs;
dev->real_num_tx_queues = txqs;
Unless there is concern, I will formally submit this later.

Thanks, Phil

\
 
 \ /
  Last update: 2016-02-17 14:21    [W:0.057 / U:0.368 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site