Robert Craig
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RE: Awful transmit performance on PPC405/Virtex. Any hope?
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Robert Craig
10/07/2008 11:21 AM
post14613
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RE: Awful transmit performance on PPC405/Virtex. Any hope?
Unfortunately, I'd have to agree with you that the networking performance is pretty abysmal. The fundamental problem I
believe has to do with the fact that the memory subsystem on that chip is very poor and there is a memory copy that
occurs between the application and the stack for data. Between that and the slowness associated with code in general
(in part, I believe, due to the memory subsystem), the performance is not good. Do you have hardware checksumming
enabled? This generally provides ~ 10-20% improvement.
Io-pkt optimizes the receive path so I wouldn't expect a large change in the transmit path. We have found some gains
in Tx speed for TCP since ACKs get Rx'ed faster, but that's not a large gain. That being said, we have seen gains of 30
-40% in receive speed for identical hardware using io-pkt, but that requires the driver to be re-written to become a
native driver rather than an io-net legacy driver that goes through the shim.
Robert.
-----Original Message-----
From: Gerald Ruescher [mailto:community-noreply@qnx.com]
Sent: Tuesday, October 07, 2008 9:24 AM
To: drivers-networking
Subject: Awful transmit performance on PPC405/Virtex. Any hope?
Hi everyone,
we're using QNX 6.3 on a 300MHz Virtex 4/PPC405 board. Networking is done with the devn-xtemac.so driver and the "old"
io-net network stack.
Unfortunately, the IP network transmit performance is really bad. With a 1000MBit interface we only get a maximum
throughput of about 6.8 MByte/sec under UDP/IP. Analysis with the Momentics profiler shows a CPU load of 100% when
sending data. Furthermore it seems that most of the time (about 80%) is spent outside the devn-xtemac driver part.
When using TCP/IP, the performance is even worse with an estimate of 4.1 MB/sec.
My questions are:
- Are these values reasonable or are we probably making some mistake regarding the low level driver? The driver is a
slightly modified version of the standard devn-xtemac.so
- Is this a situation that might improve with the new io-pkt networking stack?
Many thanks in advance for your help and kind regards,
Gerald "Jerry" Ruescher
_______________________________________________
Gerald Rüscher
Software Development Engineer
Core Real-Time Implementation
dSPACE GmbH Tel.: +49 5251 1638-1826
Technologiepark 25 Fax: +49 5251 16198-1826
33100 Paderborn http://www(dot)dspace(dot)de
Germany mailto:GRuescher(at)dspace(dot)de
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Networking Drivers
http://community.qnx.com/sf/go/post14589
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