> Well, the question is rather simple... i am running some experiments > on system with severe load on the PCI bus (basically a router with 4 interfac > es > trying to forward 2..4 streams of 64-byte packets at 100Mbit/s (i.e. 144kpps > on each stream), and from low level timing i notice that the > time to access a status register in the card sometimes goes up in the > sky (I have measured well over 10us under heavy load, whereas the > normal time is in the order of 0.5-1us). > > 10us is a fairly long time, and while i can explain it easily (there > are 4 active cards in the system, each one with a transmit, receive > and control engines trying to access the PCI bus -- and there are > two bridges between the CPU and the card), i wonder if the CPU can > potentially wait forever to get hold of the bus, or it eventually > times out. If so, how can i tell that the operation failed ?
The PCI arbitrator should never allow the system to livelock in that fashion. Furthermore, since the cards will eventually run out of descriptors/buffer space and require CPU intervention, you'll never hit that situation. And no, the CPU will not time out; it will block until it can get the bus. To Unsubscribe: send mail to [EMAIL PROTECTED] with "unsubscribe freebsd-hackers" in the body of the message
