netdev - Re: sendfile()? Re: SO_LINGER dead: I get an immediate RST on 2.6.24?

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Message-ID: <496C3D5C.7080407@hp.com>
Date:	Mon, 12 Jan 2009 23:06:04 -0800
From:	Rick Jones <rick.jones2@...com>
To:	Bill Fink <billfink@...dspring.com>
CC:	Herbert Xu <herbert@...dor.apana.org.au>,
	ilpo.jarvinen@...sinki.fi, zbr@...emap.net,
	bert.hubert@...herlabs.nl, h.willstrand@...il.com,
	netdev@...r.kernel.org
Subject: Re: sendfile()? Re: SO_LINGER dead: I get an immediate RST on 2.6.24?

Bill Fink wrote:
> On Tue, 13 Jan 2009, Herbert Xu wrote:
> 
> 
>>Bill Fink <billfink@...dspring.com> wrote:
>>
>>>If I understand you correctly, to hit this corner case, just after
>>>the final TCP write, there would have to be no packets in flight
>>>together with a zero TCP window.  To make it more bullet-proof, I
>>>guess after seeing a zero tcpi_unacked, an additional small delay
>>>should be performed, and then rechecking for a zero tcpi_unacked.
>>>I don't see anything else obvious (to me anyway) in the tcp_info
>>>that would be particularly helpful in handling this.
>>
>>What's wrong with idiag_wqueue? Isn't that a much more direct
>>way to get this?
> 
> 
> I'm not familiar with idiag_wqueue, but it sounds like it has something
> to do with INET_DIAG/INET_TCP_DIAG.  It was a long time ago, but I seem
> to recall that using INET_DIAG had a negative impact on performance,
> and since the main point of nuttcp is to measure TCP/UDP performance,
> that would be contrary to its primary purpose.  Also, I don't want to
> rely on something that's not guaranteed to be part of the running kernel.

How likely is it that the "additional small delay" above would be much 
less than waiting for a read return of zero after a shutdown(SHUT_WR) call?

rick jones
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