FreeBSD 5.3 Bridge performance take II

Gerrit Nagelhout gnagelhout at
Thu Sep 9 07:40:36 PDT 2004

Robert Watson wrote:
> Right now, though, the greatest obstacle in my immediate path 
> appears to
> be a bug in the current version of the if_em driver that causes the
> interfaces on my test box to wedge under even moderate load.  
> The if_em
> cards I have on other machines seem not to do this, which suggests a
> driver weirdness with this particular version of the chipset/card.  Go
> figure...

You may want to check the version of the chipset on that card.  There are
definitely older em cards out there which require some special alignments
on the transmitter side to avoid hangs.  If I remember correctly, the 
linux driver on the Intel web site has a workaround for this that is not
in the FreeBSD driver.  The problem is that the workaround for this 
involves splitting mbufs if the alignment isn't correct, and this is quite


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