netdev - Re: [PATCH net v2 2/3] r8152: modify the tx flow

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Message-Id: <20131104.155320.2172500441669637943.davem@davemloft.net>
Date:	Mon, 04 Nov 2013 15:53:20 -0500 (EST)
From:	David Miller <davem@...emloft.net>
To:	hayeswang@...ltek.com
Cc:	netdev@...r.kernel.org, nic_swsd@...ltek.com,
	linux-kernel@...r.kernel.org, linux-usb@...r.kernel.org
Subject: Re: [PATCH net v2 2/3] r8152: modify the tx flow

From: hayeswang <hayeswang@...ltek.com>
Date: Thu, 31 Oct 2013 13:52:38 +0800

> From: David Miller [mailto:davem@...emloft.net] 
> Sent: Thursday, October 31, 2013 5:05 AM
>> 
>> From: Hayes Wang <hayeswang@...ltek.com>
>> Date: Wed, 30 Oct 2013 15:13:39 +0800
> [...]
>> Basically, your driver will now queue up to 1,000 packets onto
>> this tx_queue list, because that is what tx_queue_len will be
>> for alloc_etherdev() allocated network devices.
>> 
>> In my previous reply to you about this patch, I asked you to
>> quantify and study the effects of using a limit of 60.  I said
>> that 60 might be too large.
>> 
>> You've responded by removing the limit completely, which is exactly
>> the opposite of what I've asked you to do.  Why did you do this?
> 
> Excuse me. My question is that the original code doesn't stop the tx queue
> either, so I don't understand why it is necessary for this patch.
> 
> I don't say I wouldn't find the suitable value for the tx queue length.
> I feel I need some time to think how to find the reasonable value. And
> I don't hope it influences the submission of the other patches, so I
> remove it first. Or, may I submit the other two patches first?

The more TX work you push into the workqueue handler, the longer the
latency for releasing the SKB and releasing all the queues that are
waiting for release of that packet.

Do you know that sockets, queueing discplines, etc. all rely upon
there being a timely release of SKBs once they are successfully
transmitted?  It must happen at the earliest moment possible that
can be reasonable obtained.

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