netdev - Re: [PATCH net-next] net: increase LL_MAX_HEADER if HYPERV

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Message-Id: <20151103.145027.1401610638879230478.davem@davemloft.net>
Date:	Tue, 03 Nov 2015 14:50:27 -0500 (EST)
From:	David Miller <davem@...emloft.net>
To:	haiyangz@...rosoft.com
Cc:	eric.dumazet@...il.com, kys@...rosoft.com, edumazet@...gle.com,
	netdev@...r.kernel.org
Subject: Re: [PATCH net-next] net: increase LL_MAX_HEADER if HYPERV_NET is
 enabled

From: Haiyang Zhang <haiyangz@...rosoft.com>
Date: Tue, 3 Nov 2015 18:49:05 +0000

>> -----Original Message-----
>> From: David Miller [mailto:davem@...emloft.net]
>> Sent: Tuesday, November 3, 2015 1:20 PM
>> To: Haiyang Zhang <haiyangz@...rosoft.com>
>> Cc: eric.dumazet@...il.com; KY Srinivasan <kys@...rosoft.com>;
>> edumazet@...gle.com; netdev@...r.kernel.org
>> Subject: Re: [PATCH net-next] net: increase LL_MAX_HEADER if HYPERV_NET
>> is enabled
>> 
>> From: Haiyang Zhang <haiyangz@...rosoft.com>
>> Date: Tue, 3 Nov 2015 17:34:47 +0000
>> 
>> > But we still keep this busy return in our code, just for "weird corner cases".
>> 
>> The queue_stopped condition must be precise.
> 
> The only case we return NETDEV_TX_BUSY is when the outgoing ring buffer is full, 
> which almost never happens because we stop the xmit queue if ring is <10% available.

I don't think you understand.

You must perform the queue stop operation such that it is impossible for your
->ndo_start_xmit() method to be invoked in a way such that you cannot transmit
the SKB given to you immediately.

It's quite tiring to keep trying to explain this over and over repeatedly.
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