netdev - Re: [PATCH 2/2 net-next] tcp: sk_add_backlog() is too agressive for TCP

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Message-ID: <1335216631.5205.71.camel@edumazet-glaptop>
Date:	Mon, 23 Apr 2012 23:30:31 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Rick Jones <rick.jones2@...com>
Cc:	David Miller <davem@...emloft.net>, netdev@...r.kernel.org,
	therbert@...gle.com, ncardwell@...gle.com, maze@...gle.com,
	ycheng@...gle.com, ilpo.jarvinen@...sinki.fi
Subject: Re: [PATCH 2/2 net-next] tcp: sk_add_backlog() is too agressive
 for TCP

On Mon, 2012-04-23 at 13:57 -0700, Rick Jones wrote:
> On 04/23/2012 01:37 PM, Eric Dumazet wrote:
> > In my 10Gbit tests (standard netperf using 16K buffers), I've seen
> > backlogs of 300 ACK packets...
> 
> Probably better to call that something other than 16K buffers - the send 
> size was probably 16K, which reflected SO_SNDBUF at the time the data 
> socket was created, but clearly SO_SNDBUF grew in that timeframe.
> 


Maybe I was not clear : Application does sendmsg() of 16KB buffers.

Yet, in the small time it takes to perform this operation, softirq can
queue up to 300 packets coming from the other side.



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