Date: Wed, 24 Oct 2001 11:59:39 -0700 From: Luigi Rizzo <rizzo@aciri.org> To: hackers@freebsd.org Subject: HW question -- can the CPU timeout on accesses to the PCI bus ? Message-ID: <20011024115939.A46082@iguana.aciri.org>
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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 interfaces 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 ? cheers luigi ----------------------------------+----------------------------------------- Luigi RIZZO, luigi@iet.unipi.it . ACIRI/ICSI (on leave from Univ. di Pisa) http://www.iet.unipi.it/~luigi/ . 1947 Center St, Berkeley CA 94704 Phone: (510) 666 2927 ----------------------------------+----------------------------------------- To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message
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