Frequent hickups on the networking layer

[Rick Macklem]

Paul Thornton wrote:
> Hi,
> 
> On 28/04/2015 22:06, Rick Macklem wrote:
> > ... If your
> > net device driver is one that allocates 9K jumbo mbufs for receive
> > instead of using a list of smaller mbuf clusters, I'd guess this is
> > what is biting you.
> 
> Apologies for the thread drift, but is there a list anywhere of what
> drivers might have this issue?
> 
If you:
# cd /usr/src/sys/dev
# find . -name "*.c" -exec fgrep -l MJUM9BYTES {} \;
you will get a hint w.r.t. which ones might have a problem. Then I
think you'll have to dig into the driver sources to see what it is
actually doing. (As you've seen on the thread Chelsio sounds like
it handles things and allows you to disable use of 9K via a tunable.)

rick
ps: Long ago (1970s) a CS prof. I had said "the sources are the only
    real documentation". I think he was correct.

> I've certainly seen performance decrease in the past between two
> machines with igb interfaces when the MTU was raised to use 9k
> frames.
> 
> Paul.
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