Re: Re: Re: limited network bandwidth with 3.2.x kernels

Eric Dumazet
2012-02-21T17:31:32Z

Le mardi 21 février 2012 à 19:19 +0200, alekcejk@googlemail.com a
écrit :
> Download speed from ftp3.de.freebsd.org increases from 5 MB/s to 10 MB/s
> after I set "sysctl net.ipv4.tcp_rmem="4096 87380 4127616""" in 3.2.7 kernel.
>
> --2012-02-21 18:56:36-- ftp://ftp3.de.freebsd.org/pub/FreeBSD/ISO-IMAGES-i386/8.2/FreeBSD-8.2-RELEASE-i386-dvd1.iso.xz
> 100%[======================================>] 2 066 424 512 10,3M/s in 3m 17s
> 2012-02-21 18:59:56 (9,99 MB/s) - «/dev/null» saved [2066424512]
>

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) still
> a bit more than in 3.2.7 - 11 MB/s instead of 10.3 MB/s.
>
> --2012-02-21 18:56:36-- ftp://ftp3.de.freebsd.org/pub/FreeBSD/ISO-IMAGES-i386/8.2/FreeBSD-8.2-RELEASE-i386-dvd1.iso.xz
> 100%[======================================>] 2 066 424 512 11,0M/s in 3m 30s
> 2012-02-21 19:13:55 (9,39 MB/s) - «/dev/null» saved [2066424512]

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.