netdev - Re: [PATCH] TCP_FAILFAST: a new socket option to timeout/abort a connection quicker

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Message-ID: <AANLkTikAGKObYnczsVoKnUOewJBp2J2036yOD7TncA0F@mail.gmail.com>
Date:	Tue, 24 Aug 2010 15:13:44 -0700
From:	Jerry Chu <hkchu@...gle.com>
To:	Hagen Paul Pfeifer <hagen@...u.net>
Cc:	Arnd Hannemann <hannemann@...s.rwth-aachen.de>,
	Eric Dumazet <eric.dumazet@...il.com>,
	ilpo.jarvinen@...sinki.fi, davem@...emloft.net,
	netdev@...r.kernel.org
Subject: Re: [PATCH] TCP_FAILFAST: a new socket option to timeout/abort a
 connection quicker

On Tue, Aug 24, 2010 at 9:28 AM, Hagen Paul Pfeifer <hagen@...u.net> wrote:
> * Arnd Hannemann | 2010-08-24 16:58:58 [+0200]:
>
>>Nice, so did you come up with a name for the socket option yet?
>
> +#define      TCP_UTO       18  /* User Timeout Option */
>
> The patch is an early state and details as well as testing is a little bit
> costly.
>
>>Hmm, is there really a difference? If an application specifies
>>a wanted timeout e.g. with USER_TIMEOUT, CHANGEABLE will
>>become false and the value would be announced via ADV_UTO.
>>The connection could be aborted locally after that time passed,
>>regardless of what the remote site thinks the timeout should be.
>>
>>As I understand it U_LIMIT and L_LIMIT would only be there
>>for safety to disallow nonsensical values of USER_TIMEOUT.
>>
>>Did I miss something?
>
> Maybe not, aot sure. I must take a look at the patch from Jerry. I had no time
> until now.

According to RFC5482
"Decreasing the user timeouts allows busy servers to explicitly notify
their clients that they will maintain the connection state only for a
short time without connectivity."

So it looks like the user timeout can be used in either senario (shortening
or lengthening) and in both cases is a lower bound, i.e., the connection
should abort at or shortly after the specified user timeout.

In this case does it make sense to combine the two? Will your TCP_UTO
patch be ready anytime soon?

Again an alternative is to allow configuring tcp_retries2 and TCP_RTO_MAX
directly. I'm open to suggestion but we'd like to get something in sooner.

Thanks,

Jerry

>
> Hagen
>
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