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

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Date:	Mon, 14 Apr 2014 00:19:14 -0400
From:	Steven Galgano <sgalgano@...acentlink.com>
To:	David Miller <davem@...emloft.net>
CC:	mst@...hat.com, jasowang@...hat.com, xemul@...allels.com,
	wuzhy@...ux.vnet.ibm.com, therbert@...gle.com, yamato@...hat.com,
	richardcochran@...il.com, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, Brian.Adamson@....navy.mil,
	jgiovatto@...acentlink.com
Subject: Re: [PATCH v2] tuntap: add flow control to support back pressure

On 04/13/2014 09:40 PM, David Miller wrote:
> From: Steven Galgano <sgalgano@...acentlink.com>
> 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 <brian.adamson@....navy.mil>
>> Tested-by: Joseph Giovatto <jgiovatto@...centlink.com>
>> Signed-off-by: Steven Galgano <sgalgano@...acentlink.com>
> 
> 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 <brian.adamson@....navy.mil>
Tested-by: Joseph Giovatto <jgiovatto@...centlink.com>
Signed-off-by: Steven Galgano <sgalgano@...acentlink.com>


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