netdev - Re: initial congestion window for connections in the listen queue

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]

Message-Id: <20090413.142653.267913010.davem@davemloft.net>
Date:	Mon, 13 Apr 2009 14:26:53 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	opurdila@...acom.com
Cc:	netdev@...r.kernel.org
Subject: Re: initial congestion window for connections in the listen queue

From: Octavian Purdila <opurdila@...acom.com>
Date: Mon, 13 Apr 2009 23:46:15 +0300

> 
> A question for the TCP wizards:
> 
>>struct sock *tcp_create_openreq_child(struct sock *sk, 
>>        struct request_sock >*req, struct sk_buff *skb)
>>{
>>...
>>         /* So many TCP implementations out there (incorrectly) count the
>>          * initial SYN frame in their delayed-ACK and congestion control
>>          * algorithms that we must have the following bandaid to talk 
>>          * efficiently to them.  -DaveM
>>          */
>>          newtp->snd_cwnd = 2;
> 
> Shouldn't the same logic from tcp_init_cwnd() be used here?
> 
>>>From my traces, this seems to prevent TSO from helping short lived 
> connections.

On any standard ethernet MTU or larger, you should be getting
an initial CWND of 3 or 4 because of the logic in tcp_init_cwnd().

Don't just guesstimate what initial ->snd_cwnd value the
kernel is using by looking casually at tcpdump traces.  Add
some kernel debugging printk's and find out for sure.
--
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