BeagleBone slow inbound net I/O

[Tim Kientzle]

> On Mar 14, 2015, at 12:15 AM, Brett Wynkoop <freebsd-arm at wynn.com> wrote:
> 
> [wynkoop at beaglebone ~]$ sysctl dev.cpsw | grep -i error
> dev.cpsw.0.stats.RxCrcErrors: 262
> dev.cpsw.0.stats.RxAlignErrors: 231
> dev.cpsw.0.stats.CarrierSenseErrors: 0
> [wynkoop at beaglebone ~]$ 
> 
> So we can see climbing errors.  I am not sure how this compares to the
> results of others. The above was during the first few minutes of a
> buildworld from an nfs share.

Your Ethernet hardware is detecting a lot of low-level network
errors, which generally indicates hardware problems in your
network:  a bad cable maybe, or a dying switch or bad power
supply.

In any event, NFS throughput degrades rapidly on a poor
network, so this probably explains your NFS slowness.

There are a lot of error-related counters that aren’t called Errors,
by the way.  In particular, the various collision and overrun
counters don’t actually have “Error” in the name.

On my BeagleBones, the only non-zero error counter I generally
see is the RxStartOfFrameOverruns.

Tim