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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Tue, 24 Aug 2010 14:56:28 -0700
From:	Jerry Chu <hkchu@...gle.com>
To:	Arnd Hannemann <hannemann@...s.rwth-aachen.de>
Cc:	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 1:04 AM, Arnd Hannemann
<hannemann@...s.rwth-aachen.de> wrote:
> Am 24.08.2010 08:44, schrieb Eric Dumazet:
>> Le lundi 23 août 2010 à 23:20 -0700, H.K. Jerry Chu a écrit :
>>> From: Jerry Chu <hkchu@...gle.com>
>>>
>>> This is a TCP level socket option that takes an unsigned int to specify
>>> how long in ms TCP should resend a lost data packet before giving up
>>> and returning ETIMEDOUT. The normal TCP retry/abort timeout limit still
>>> applies. In other words this option is only meant for those applications
>>> that need to "fail faster" than the default TCP timeout. The latter
>>> may take upto 20 minutes in a normal WAN environment.
>>>
>>> The option is disabled (by default) when set to 0. Also it does not
>>> apply during the connection establishment phase.
>>>
>>> Signed-off-by: H.K. Jerry Chu <hkchu@...gle.com>
>>
>> TCP_FAILFAST might be misleading. It reads as a boolean option, while
>> its an option to cap the timeout, with a time unit, instead of the usual
>> "number of retransmits".
>
> Why not call it TCP_USERTIMEOUT?

Sure, except that it was designed to shorten the system default user timeout,
not lengthen it. (But perhaps it can be combined with TCP_UTO?)

The current default user timeout of 13-20minutes in Linux may be adequate for
some apps but too long for many others. A per connection socket option solves
this problem.

> Later you can also send it via the TCP user timeout option... (RFC5482)
> Hmm... is the ms granularity really needed? Does it make sense to abort
> a connection below a second?

Yes I thought about that too, but decided it's better to allow the
flexibility of sub-
sec level timeout for possible future usage in HPC type of applications, rather
than to regret later.

>
>> Its also funny you dont ask for a default value, given by a sysctl
>> tunable ;)
>
> Well retries1/2 would be the tunables, no?

The was my first thought, to allow tcp_retries2 to be reduced on a per
connection basis. But I also see a need to reduce TCP_RTO_MAX in
order to allow a reasonable # of retries, given a shorter timeout.

I saw a patch submitted a couple of months ago to allow tcp_retries2 to be
configured but haven't seen any forward progress on the patch. If people
think letting apps configure tcp_retries2 and TCP_RTO_MAX directly is
a better solution I'm for it too.

Thanks,

Jerry

>
> Best regards,
> Arnd
>
--
To unsubscribe from this list: send the line "unsubscribe netdev" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html