netdev - Re: RFC: Nagle latency tuning

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:	Mon, 08 Sep 2008 23:02:21 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	csnook@...hat.com
Cc:	rick.jones2@...com, netdev@...r.kernel.org
Subject: Re: RFC: Nagle latency tuning

From: Chris Snook <csnook@...hat.com>
Date: Tue, 09 Sep 2008 01:56:12 -0400

[ Please hit enter every 80 columns or so, your emails are
  unreadable until I reformat your text by hand, thanks. ]

> That's not the problem I'm talking about here.  The problem I'm
> seeing is that if your burst of messages is too small to fill the
> MTU, the network stack will just sit there and stare at you for
> precisely 40 ms (an eternity for a financial app) before
> transmitting.  Andi may be correct that it's actually the delayed
> ACK we're seeing, but I can't figure out where that 40 ms magic
> number is coming from.
>
> The easiest way to see the problem is to open a TCP socket to an
> echo daemon on loopback, make a bunch of small writes totaling less
> than your loopback MTU (accounting for overhead), and see how long
> it takes to get your echoes.  You can probably do this with netcat,
> though I haven't tried.  People don't expect loopback to have 40 ms
> latency when the box is lightly loaded, so they'd really like to
> tweak that down when it's hurting them.

That's informative, but please provide a specific test case and
example trace so we can discuss something concrete.

Thank you.
--
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