Date: Mon, 06 Nov 2000 22:46:09 +0000 From: Brian Somers <brian@Awfulhak.org> To: Kris Kennaway <kris@FreeBSD.ORG> Cc: "Richard A. Steenbergen" <ras@e-gerbil.net>, David Greenman <dg@root.com>, freebsd-net@FreeBSD.ORG, brian@Awfulhak.org Subject: Re: tcp sendspace/recvspace Message-ID: <200011062246.eA6Mk9T13715@hak.lan.Awfulhak.org> In-Reply-To: Message from Kris Kennaway <kris@FreeBSD.org> of "Sun, 05 Nov 2000 17:57:22 PST." <20001105175722.A8886@citusc17.usc.edu>
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> On Sun, Nov 05, 2000 at 08:36:14PM -0500, Richard A. Steenbergen wrote:
> > On Sun, 5 Nov 2000, Kris Kennaway wrote:
> >=20
> > > On Sun, Nov 05, 2000 at 02:02:44PM -0800, David Greenman wrote:
> > > > I've been messing around with the net.inet.tcp.sendspace and=20
> > > > net.inet.tcp.recvspace parameters on ftp.freesoftware.com and have fo=
> und
> > > > that there is a significant performance improvement when increasing t=
> hese
> > > > to 32768 bytes. Apparantly there are enough systems out there with hi=
> gher
> > > > window maxes that it really does make a difference. By significant=20
> > > > improvement, I mean about a average of a 20% increase in Mbps per use=
> r,
> > > > and this was just the change over a 30 minute period with lots of con=
> nections
> > > > still using the old 16K values.
> > > > Any objections to increasing the defaults in FreeBSD to 32K?
> > >=20
> > > Won't this impact the latency of multiple connections over a slow PPP l=
> ink?
> >=20
> > Thats what the congestion window is for. Any limitation of transmits based
> > on the advertised memory limitation window is totally improper.
>
> Perhaps it was a bug, but I used to see e.g. FTP transfers which were
> running at full speed totally monopolizing my modem bandwidth (then a
> 14.4k), and other sessions not being able to receive their "fair
> share". Tweaking net.inet.tcp.recvspace to give only a second or two
> worth of data transfer reduced the latency to acceptable levels.
>
> Maybe this has been fixed by now - I haven't noticed it since I
> upgraded to a 56k modem. I'll try increasing my system to 32768
> and see if it has any effect.
Have a look at ppp's ``set urgent'' and ``set ifqueue'' commands.
These will effect interactive performance over a (slow) link....
Setting tcp.sendspace to a low value would probably make these ppp
values more sensitive.
> Kris
--
Brian <brian@Awfulhak.org> <brian@[uk.]FreeBSD.org>
<http://www.Awfulhak.org>; <brian@[uk.]OpenBSD.org>
Don't _EVER_ lose your sense of humour !
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