Automatic TCP send and receive socket buffer sizing
chrcoluk at gmail.com
Thu Dec 14 16:55:21 PST 2006
On 14/12/06, Andre Oppermann <andre at freebsd.org> wrote:
> Chris wrote:
> > On 12/12/06, Andre Oppermann <andre at freebsd.org> wrote:
> >> This is a patch adding automatic TCP send and receive socket buffer
> >> sizing.
> >> Normally the socket buffers are static (either derived from global
> >> defaults
> >> or set with setsockopt) and do not adapt to real network conditions. Two
> >> things happen: a) your socket buffers are too small and you can't
> >> reach the
> >> full potential of the network between both hosts; b) your socket
> >> buffers are
> >> too big and you waste a lot of kernel memory for data just sitting
> >> around.
> >> With automatic TCP send and receive socket buffers we can start with a
> >> small
> >> buffer and quickly grow it in parallel with the TCP congestion window
> >> to match
> >> real network conditions.
> >> FreeBSD has a default 32K send socket buffer. This supports a maximal
> >> transfer rate of only slightly more than 2Mbit/s on a 100ms RTT trans-
> >> continental link. Or at 200ms just above 1Mbit/s. With TCP send buffer
> >> auto scaling and the default values below it supports 20Mbit/s at 100ms
> >> and 10Mbit/s at 200ms. That's an improvement of factor 10, or 1000%.
> >> For the receive side it looks slightly better with a default of 64K
> >> buffer
> >> size.
> >> The automatic send buffer sizing patch is currently running on one
> >> half of
> >> the FTP.FreeBSD.ORG cluster w/o any problems so far. Against this
> >> machine
> >> with the automatic receive buffer sizing patch I can download at
> >> 5.7MBytes
> >> per second. Without patch it maxed out at 1.6MBytes per second as the
> >> delay
> >> bandwidth product became equal to the static socket buffer size
> >> without hitting
> >> the limits of the physical link between the machines. My test machine
> >> is about
> >> 35ms from that FTP.FreeBSD.ORG and connected through a moderately
> >> loaded 100Mbit
> >> Internet link.
> >> New sysctl's are:
> >> net.inet.tcp.sendbuf_auto=1 (enabled)
> >> net.inet.tcp.sendbuf_inc=8192 (8K, step size)
> >> net.inet.tcp.sendbuf_max=262144 (256K, growth limit)
> >> net.inet.tcp.recvbuf_auto=1 (enabled)
> >> net.inet.tcp.recvbuf_inc=16384 (16K, step size)
> >> net.inet.tcp.recvbuf_max=262144 (256K, growth limit)
> >> The patch is available here (it may apply with some fuzz):
> >> http://people.freebsd.org/~andre/tcp_auto_buf-20061212.diff
> >> Any tests and test reports are very welcome.
> >> --
> >> Andre
> > Hi does this patch work on 6.x? I used the send patch on 6.x and works
> > great please make a 6.x patch thank you and I will happily test.
> No, this patch doesn't work on 6.x. It makes changes to struct tcpcb
> to add two additional fields. This requires netstat(1) to be recompiled
> and is a ABI change. However I've got a number of requests for 6.x
> patch so I may make one anyway.
Please that would be great, the send patch works on 6.x flawlessly and
has improved performance enormously it would be a shame to have to
wait for 7.x to be production ready before I use it.
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