netdev - Re: [Linux-ATM-General] [PATCH] atm/br2684: netif_stop_queue() when atm device busy and netif_wake

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Date:	Tue, 15 Sep 2009 15:44:53 +0200
From:	Karl Hiramoto <karl@...amoto.org>
To:	David Miller <davem@...emloft.net>
Cc:	philipp_subx@...fish-solutions.com, netdev@...r.kernel.org,
	linux-atm-general@...ts.sourceforge.net
Subject: Re: [Linux-ATM-General] [PATCH] atm/br2684: netif_stop_queue() when
 atm device busy and netif_wake_queue() when we can send packets again.

David Miller wrote:
> From: Karl Hiramoto <karl@...amoto.org>
> Date: Thu, 10 Sep 2009 23:30:44 +0200
>
>   
>> I'm not really sure if or how many packets to upper layers buffer.
>>     
>
> This is determined by ->tx_queue_len, so whatever value is being
> set for ATM network devices is what the core will use for backlog
> limiting while the device's TX queue is stopped.
I tried varying tx_queue_len by 10, 100,  and 1000x, but it didn't seem 
to help much.  Whenever the atm dev called netif_wake_queue() it seems 
like the driver still starves for packets  and still takes time to get 
going again.


It seem like when the driver calls netif_wake_queue() it's TX hardware 
queue is nearly full, but it has space to accept new packets.  The TX 
hardware queue has time to empty, devices starves for packets(goes 
idle), then finally a packet comes in from the upper networking 
layers.   I'm not really sure at the moment where the problem lies to my 
maximum throughput dropping.

I did try changing sk_sndbuf to 256K but that didn't seem to help either.

--
Karl
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