realtek performance (was Re: good ATI chipset results)

Sean McNeil sean at
Thu Oct 13 10:07:41 PDT 2005

On Thu, 2005-10-13 at 11:49 -0400, John Baldwin wrote:
> On Thursday 13 October 2005 11:13 am, Sean McNeil wrote:
> > On Thu, 2005-10-13 at 09:17 -0400, Mike Tancsa wrote:
> > > Havent really seen anyone else use this board, but I have had good
> > > luck with it so far
> > >
> > >
> > >nuID=90&LanID=0
> > >
> > > Its a micro ATX formfactor with built in video and the onboard NIC is
> > > a realtek.  (Although its not the fastest NIC, its driver is stable
> > > and mature-- especially compared to the headaches people seem to have
> > > with the NVIDIA NICs.)
> >
> > Is this the RealTek 8169S Single-chip Gigabit Ethernet?
> >
> > For those interested, here are some changes I always use to increase the
> > performance of the above NIC.  With these mods, I can stream over 20
> > MBps video multicast and do other stuff over the network without issues.
> > Without the changes, xmit is horrible with severe UDP packet loss.
> So, I see two changes.  One is to up the number of descriptors from 32 rx and 
> 64 tx to 64 rx and 64 tx on some models and 1024 rx and 1024 tx on other 
> modules.  The other thing is that you seem to pessimize TX performance by 
> always forcing the send packets to be coalesced into one mbuf (which requires 
> doing an alloc and then copying all of the data) instead of making use of 
> scatter/gatter for sending packets.  Do you need both changes or do just the 
> higher descriptor counts make the difference?

Actually, I've found that the higher descriptor counts do not make a
noticeable difference.  The only thing that mattered was to eliminate
the scatter/gather of sending packets.  I can't remember why I left the
descriptor increase in there.  I think it was to get the best use out of
the hardware.


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