Re: Brust data send problem on gigabit NIC on Linux

[Ben Greear <greearb@candelatech.com>]

Lk Overrun wrote:
> Hi, I am seeking advice on how to best send out huge
> number of packets on a gigabit ethernet interface.  I
> am using kernel 2.4.19.  I try to send out as many as
> possible 15Kbyte-long ethernet packets to try to
> utilize the giga-bit/sec bandwidth.  My CPU is really
> fast (2 GHz) amd I dump the packets to the interface
> in a  tight loop in user space.  However, I can only
> reach around 400 Mbits/sec before the packets get
> dropped.  The queue discipline (qdisc) seems to be
> responsible because the queue length (txqueuelen) is
> only 100 by default, and the queue just cannot store
> so many packets at once.  I can eliminate the packet
> drop by raising the queue length to somewhere like
> 60000 but that is not practical because it uses too
> much memory. It seems I need some delay between
> sending packets but I cannot sleep for less than 10 ms
> (1/Hz) in user space and 10 ms is too long.
> 
> I am using raw socket bypassing the IP stack and my
> NIC is the Intel Pro1000 (using the e1000.o driver).
> 
> What is the best way to send raw ethernet packets,
> reaching gigabit range withuut packet drop on Linux? 
> Thanks for any advice.

Make sure the e1000 driver is tuned, try insmodding it with:
TxDescriptors=1024 RxDescriptors=4096

Also, in your user-space app, check the return code of your
packet-sending call.  That can let you know that the kernel
dropped it, and that you need to re-send.

How do you know you are dropping packets?  (Ie, are you also
reading on another machine?)  Usually it's read that drops
more packets than write.

Good luck,
Ben

> 
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-- 
Ben Greear <greearb@candelatech.com>       <Ben_Greear AT excite.com>
President of Candela Technologies Inc      http://www.candelatech.com
ScryMUD:  http://scry.wanfear.com     http://scry.wanfear.com/~greear