From mboxrd@z Thu Jan  1 00:00:00 1970
From: Eric Dumazet <eric.dumazet@gmail.com>
Subject: Re: Re: Re: limited network bandwidth with 3.2.x kernels
Date: Tue, 21 Feb 2012 18:31:24 +0100
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Le mardi 21 f=C3=A9vrier 2012 =C3=A0 19:19 +0200, alekcejk@googlemail.c=
om a
=C3=A9crit :
> Download speed from ftp3.de.freebsd.org increases from 5 MB/s to 10 M=
B/s
> after I set "sysctl net.ipv4.tcp_rmem=3D"4096 87380 4127616""" in 3.2=
=2E7 kernel.
>=20
> --2012-02-21 18:56:36--  ftp://ftp3.de.freebsd.org/pub/FreeBSD/ISO-IM=
AGES-i386/8.2/FreeBSD-8.2-RELEASE-i386-dvd1.iso.xz
> 100%[=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D>] 2 066 424 512 10,3M/=
s  in 3m 17s
> 2012-02-21 18:59:56 (9,99 MB/s) - =C2=AB/dev/null=C2=BB saved [206642=
4512]
>=20

Yep, this confirms the thing. You were at the limit of optimal receiver
window. Find a more remote server (80ms rtt for example) and you'll see
that your default tcp_rmem[2] was too small, even on 3.1.10 kernel.

> But maximum speed in 3.1.10 kernel (without this sysctl settings) sti=
ll
> a bit more than in 3.2.7 - 11 MB/s instead of 10.3 MB/s.
>=20
> --2012-02-21 18:56:36--  ftp://ftp3.de.freebsd.org/pub/FreeBSD/ISO-IM=
AGES-i386/8.2/FreeBSD-8.2-RELEASE-i386-dvd1.iso.xz
> 100%[=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D>] 2 066 424 512 11,0M/=
s   in 3m 30s  =20
> 2012-02-21 19:13:55 (9,39 MB/s) - =C2=AB/dev/null=C2=BB saved [206642=
4512]

Thats one measure, you'll have to make a lot of different measures to
make this significant, preferably in a lab to rule out different
external network conditions.