[Bloat] SO_SNDBUF and SO_RCVBUF

[Eric Dumazet]

Yeah, the real nice thing is TCP_NOTSENT_LOWAT added in linux-3.12




On Wed, 2015-04-22 at 12:28 -0700, Dave Taht wrote:
> SO_SNDLOWAT or something similar to it with a name I cannot recall,
> can be useful.
> 
> On Wed, Apr 22, 2015 at 12:10 PM, Hal Murray <hmurray at megapathdsl.net> wrote:
> >
> >> As I understand it (I thought) SO_SNDBUF and SO_RCVBUF are socket buffers
> >> for the application layer, they do not change the TCP window size either
> >> send or receive. Which is perhaps why they aren't used much. They don't do
> >> much good in iperf that's for sure! Might be wrong, but I agree with the
> >> premise - auto-tuning should work.
> >
> > I sure expect them to do the obvious thing.
> >
> > man 7 socket says:
> >
> >        SO_SNDBUF
> >               Sets  or gets the maximum socket send buffer in bytes.
> >
> > It doesn't actually say that turns into the TCP window size.
> >
> > On Linux, there is a factor of 2 for overhead and whatever.
> >
> > man tcp says:
> >       TCP uses the extra space for administrative purposes and inter-
> >        nal kernel structures, and the /proc file  values  reflect  the  larger
> >        sizes  compared  to the actual TCP windows.
> >
> > So it looks like the number you feed it turns into the window size.
> >
> > A few quick tests with netperf confirm that it is doing something close to
> > what I expect but I haven't fired up tcpdump to verify that the window size
> > is what I asked for.  netperf does print out values that are 2x what I asked
> > for.
> >
> > Yuck.  (That's Yuck at Linux, not netperf.)
> >
> >
> > --
> > These are my opinions.  I hate spam.
> >
> >
> >
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> 
>