[AG-TECH] Mac buffer tweak?

[Piers O'Hanlon]

Hi,

I think the key sysctl here is this one: kern.ipc.maxsockbuf=8000000
which determines the max UDP buffer sizes (the others, as Chris points
out, are only relevant to TCP).

What would be useful to check is to run netstat -s on your system with
and without the ker.ipc.maxsocketbuf setting - and look at the UDP
section on "dropped due to full socket buffers" and see how this
changes.

However this is odd as vic does set the socket buffer sizes in the
application. One explanation maybe that the application provided
buffer sizes are a guide and if they're overrun then it can use more
memory but if the default max (on my MacBook they're set to 262144) is
too low then they will run out and hence you'll get bad video.

The other thing that is strange is that this doesn't appear to happen
on Linux (maybe it is and we haven't noticed it) but after a quick
look at the Linux kernel it seems that the SO_RCVBUF setsocketopt()
kernel implementation doubles the supplied value which may makes
things ok on Linux? However the max buffer size in Linux (Ubuntu 7.10
anyway) is /proc/sys/net/core/wmem_max 131071 (which is lower than
OSX)...

If we find that vic's default's are too low then we can tweak them,
though it may only be fixed on some systems but increasing the system
maximum.....

It maybe worth keeping an eye on UDP buffer overruns (use netstat -s)
to see if this a more general problem.

There's a good guide on UDP buffer sizing here:
http://www.29west.com/docs/THPM/udp-buffer-sizing.html

Piers.


On 10/11/2007, gurcharan khanna <gskpop at cis.rit.edu> wrote:
> Christoph Willing wrote:
> >
> > On 10/11/2007, at 7:56 AM, gurcharan khanna wrote:
> >
> >> Mark,
> >>
> >> my link to the source for this seems to be broken but here's what i
> >> have personally on my mac.
> >>
> >> in /etc/sysctl.conf, add these lines:
> >>
> >>
> >> net.inet.tcp.recvspace=4000000
> >> net.inet.tcp.sendspace=4000000
> >> kern.ipc.maxsockbuf=8000000
> >
> >
> > Those settings look like they may have come from:
> >     http://www.psc.edu/networking/projects/tcptune/
> You're right about the URL. However, the link doesn't work anymore....
> >
> > However, note that TCP tuning is the subject there, not UDP (which is
> > what multicast uses).
> Understood. However, changing these settings DOES in fact improve things
> considerably, predictably,
> and repeatedly. I don't quite understand it, but it does work.
>
> -gurcharan
> >
> >
> > chris
> >
> >
> >
> >> you probably have to restart to activate them. you can set these from
> >> the command line as well but they won't "stick", but you can try out
> >> different
> >> settings that way.
> >>
> >> use: sysctl -w net.inet.tcp.recvspace=4000000        (for example)
> >>
> >> to set these values interactively.
> >>
> >> -gurcharan
> >>
> >>
> >>
> >> Leonard, Mark wrote:
> >>> Listers--
> >>>
> >>> It was probably a year ago that a setting change for Mac OS that
> >>> improved video quality of big video multicast streams (Gurcharan?)
> >>> but I
> >>> can't seem to find it any where...
> >>>
> >>> Can someone repost or point me towards a troubleshooting page for
> >>> tweaks
> >>> like this?
> >>>
> >>> Thanks
> >>> Mark
> >>>
> >>>
> >>> Mark Leonard
> >>> DL Studios, UNH
> >>> 603-862-0192
> >>>
> >>>
> >>>
> >>>
> >>>
> >>
> >> --
> >> -------------------------
> >> Gurcharan S. Khanna, Ph.D.
> >> Director of Research Computing
> >> Office of the Vice President for Research
> >>
> >> Director, Interactive Collaboration Environments Laboratory,
> >> Center for the Advancing the Study of Cyberinfrastructure
> >> ---
> >> Rochester Institute of Technology
> >> 1 Lomb Memorial Drive
> >> Rochester, New York 14623-5603
> >> Phone: 585-475-7504  ~  Cell: 585-451-8370
> >> Email: gurcharan.khanna at rit.edu
> >> Http:  people.rit.edu/gskpop
> >>
> >
> > Christoph Willing                       +61 7 3365 8350
> > QCIF Access Grid Manager
> > University of Queensland
> >
> >
> >
>
>
> --
> -------------------------
> Gurcharan S. Khanna, Ph.D.
> Director of Research Computing
> Office of the Vice President for Research
>
> Director, Interactive Collaboration Environments Laboratory,
> Center for the Advancing the Study of Cyberinfrastructure
> ---
> Rochester Institute of Technology
> 1 Lomb Memorial Drive
> Rochester, New York 14623-5603
> Phone: 585-475-7504  ~  Cell: 585-451-8370
> Email: gurcharan.khanna at rit.edu
> Http:  www.rit.edu/~gskpop
>
>