[AG-TECH] Mac buffer tweak?

[Piers O'Hanlon]

Hi Gurcharan,

Thanks for the clarification.

> To be precise, the only reason I have manipulated these parameters is to
> be able to render  the 19.2 Mbps mpeg2 stream from Seattle (233.0.73.26)
> with VLC and similar higher throughput
> streams. I never had a problem with vic streams, so my experiments and
> observations reflected the need to optimize at higher bitrates.
>
Right that would make sense - It should only be an issue at higher data rates.

> However, I also played around with these settings at home with my
> wireless connection via Airport to roadrunner cable modem internet access,
> so I was interested in optimizing both tcp and udp. I also seem to recall
> something about the maxsockbuf being large enough to accommodate the tcp
> send/recv space settings, but perhaps that was inaccurate.
>
Ok fine - yes there are a number of web pages out there about TCP
tuning which suggest these sort of tweaks for high bandwidth etc. This
one being quite good:
http://www.macgeekery.com/tips/configuration/mac_os_x_network_tuning_guide_revisited

Piers.

> Fyi,
>
> -gurcharan
>
> Piers O'Hanlon wrote:
> > 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
> >>
> >>
> >>
>
>
> --
> -------------------------
> 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
>
>