Subject: Re: [PATCH v2] tuntap: add flow control to support back pressure

From: Steven Galgano <[email-masked]>
Date: Mon, 14 Apr 2014 00:19:14 -0400

On 04/13/2014 09:40 PM, David Miller wrote:
> From: Steven Galgano <[email-masked]>
> Date: Sun, 13 Apr 2014 21:30:27 -0400
> 
>> Added optional per queue flow control support using IFF_FLOW_CONTROL. When the IFF_FLOW_CONTROL TUNSETIFF flag is specified it will set a per queue flag to indicate that the queue should be stopped using netif_tx_stop_queue(), rather than discarding frames once full. After reading a frame from the respective stopped queue, a netif_tx_wake_queue() is issued to signal resource availability.
>>
>> The per queue TUN_FLOW_CONTROL flag is stored in struct tun_file. This provides the flexibility to enable flow control on all, none or some queues when using IFF_MULTI_QUEUE. When not using IFF_MULTI_QUEUE, IFF_FLOW_CONTROL will apply to the single queue. No changes were made to the default drop frame policy.
>>
>> This change adds support for back pressure use cases.
>>
>> Reported-by: Brian Adamson <[email-masked]>
>> Tested-by: Joseph Giovatto <[email-masked]>
>> Signed-off-by: Steven Galgano <[email-masked]>
> 
> Please format your commit messages to ~80 columns of text.
> 
> It won't be automatically formatted by GIT and in fact it looks ugly
> with all the wrapping in text based tools.
> 
Added optional per queue flow control support using IFF_FLOW_CONTROL. When the 
IFF_FLOW_CONTROL TUNSETIFF flag is specified it will set a per queue flag to 
indicate that the queue should be stopped using netif_tx_stop_queue(), rather 
than discarding frames once full. After reading a frame from the respective 
stopped queue, a netif_tx_wake_queue() is issued to signal resource 
availability.

The per queue TUN_FLOW_CONTROL flag is stored in struct tun_file. This provides 
the flexibility to enable flow control on all, none or some queues when using 
IFF_MULTI_QUEUE. When not using IFF_MULTI_QUEUE, IFF_FLOW_CONTROL will apply to 
the single queue. No changes were made to the default drop frame policy.

This change adds support for back pressure use cases.

Reported-by: Brian Adamson <[email-masked]>
Tested-by: Joseph Giovatto <[email-masked]>
Signed-off-by: Steven Galgano <[email-masked]>