Re: limited network bandwidth with 3.2.x kernels

Bill Fink
2012-02-15T07:52:03Z

On Wed, 15 Feb 2012, Eric Dumazet wrote:

> Le mercredi 15 février 2012 à 01:03 -0500, Neal Cardwell a écrit :
> > There are some potentially interesting differences in sysctl values:
> >
> > > diff -u /tmp/sysctl-a-3.1.txt /tmp/sysctl-a-3.2.txt | grep mem_def
> > -net.core.wmem_default = 114688
> > -net.core.rmem_default = 114688
> > +net.core.wmem_default = 163840
> > +net.core.rmem_default = 163840
> >
> > Can you please try running this as root on the 3.2 kernel and then see
> > what sort of performance you get:
> >
> > sysctl net.core.rmem_default=114688
> >
> > This should make the 3.2 config closer to the 3.1 config. Should be
> > interesting to see if the behavior is more similar when that happens.
> >
> > neal
>
> These changes are normal, since skb truesize now include shared_info.
>
> By the way, these params are not used for tcp streams.
>
> This is why I asked netstat -s values, to check if we had drops because
> of truesize limits.
>
> Its not the case here since skb are not too fat (as some NICS can do,
> using a full PAGE to hold a single 1500 bytes frams)

Would it be useful to check if there was any difference in
TCP parameters between the 3.1 and 3.2 kernels by performing
the following on each:

grep . /sys/module/tcp_*/parameters/*

-Bill