netdev - Re: [PATCH net-next 2/3] mlx4_en: moderate frequency of TX completions

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Date:	Thu, 23 Feb 2012 16:46:42 -0500 (EST)
From:	David Miller <davem@...emloft.net>
To:	bhutchings@...arflare.com
Cc:	yevgenyp@...lanox.co.il, netdev@...r.kernel.org
Subject: Re: [PATCH net-next 2/3] mlx4_en: moderate frequency of TX
 completions

From: Ben Hutchings <bhutchings@...arflare.com>
Date: Thu, 23 Feb 2012 21:13:56 +0000

> On Thu, 2012-02-23 at 14:44 -0500, David Miller wrote:
>> From: Yevgeny Petrilin <yevgenyp@...lanox.co.il>
>> Date: Thu, 23 Feb 2012 15:34:27 +0200
>> 
>> > No need to ask for completion for every packet being sent.
>> > So the method is to ask for a completion every 16 packets,
>> > or when the queue is about to be full.
>> > 
>> > Signed-off-by: Yevgeny Petrilin <yevgenyp@...lanox.co.il>
>> 
>> You absolutely cannot do this, you must signal completion and free up
>> TX queue packets in a finite amount of time.
> 
> Really, sfc has been doing this forever.

You have to stop, because otherwise sockets can hang since those
packets can hold a reference to the socket so they must be
released in a finite amount of time regardless of network
traffic.
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