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

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Message-ID: <4F95CECF.6030901@hp.com>
Date:	Mon, 23 Apr 2012 14:51:11 -0700
From:	Rick Jones <rick.jones2@...com>
To:	Eric Dumazet <eric.dumazet@...il.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 04/23/2012 02:30 PM, Eric Dumazet wrote:
> On Mon, 2012-04-23 at 13:57 -0700, Rick Jones wrote:
>> 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.

I'd probably call that a 16K send test.  The root of the issue being 
there being "send buffers" and "send socket buffers" (and their receive 
versions).

My "canonical" test - at least one that appears in most of my 
contemporary scripts uses a 64K send size for the bulk transfer tests. 
I switch back-and-forth between tests which allow the socket buffer size 
to be determined automagically, and those where I set both sides' socket 
buffers to 1M via the test-specific -s and -S options.  In "netperf 
speak" those would probably be "x64K" and "1Mx64k" respectively.  More 
generally "<socket buffer size>x<send size>" (I rarely set/specify the 
receive size in those tests, leaving it at whatever SO_RCVBUF is at the 
start.

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

There is more to it than just queue-up 16 KB right?

rick
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