# nfe_defrag() routine in nividia ethernet driver



## huhu (Dec 17, 2010)

Hi, we ported the nvidia ethernet driver to our product and recently ran into error condition that packets would get dropped quietly.  The root cause resides in the nfe_encap() routine, where we call nfe_defrag() to try to reduce the length of the mbuf chain to 32, if it's longer than 32.  In the event the 32 mbufs need more than 32 segments, the subsequent call to bus_dmamap_load_mbuf_sg() would cause it to return an error then the packet is subsequently dropped.  

My questions are,

1. there appears to be a generic m_defrag() routine available, which doesn't stop at 32 and is used by a couple of other drivers (Intel, Broadcom, to name a few).  What was the need for a nvidia version of the defrag routine?

2. The NFE_MAX_SCATTER, which limits how many segments can be used, constant is defined to be 32, while the corresponding constants for other drivers are 100 or 64 (again Intel or Broadcom).  How was the value 32 picked?  Anybody knows the reasoning behind them?

Thanks,
mc


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## DutchDaemon (Dec 17, 2010)

This sounds like an issue for the FreeBSD mailing lists, where most of the developers hang out.


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## huhu (Dec 17, 2010)

DutchDaemon said:
			
		

> This sounds like an issue for the FreeBSD mailing lists, where most of the developers hang out.



Thanks, i'll post my questions there then.


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