Date: 17 Jul 1996 20:29:19 +0200 From: "Stefan Bethke" <stefan@Promo.DE> To: "Dennis" <dennis@etinc.com> Cc: hackers@freebsd.org Subject: Re: mitsumi CD-ROM Message-ID: <n1374487071.58218@quick.Promo.DE>
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> stealing the bus is stealing the cpu when a router is doing largely > transfers from cards. Your cant process packets until you get them. And if > the cpu is in a transfer cycle and cant get the bus then its idle. > > I dont want my packet transfers being interrupted by trivial disk activity. > An IDE will only use the CPU when it has it already anyway.....a > bus-master makes the system much less predictable and assumes the wrong > priorities. The priorities are independent of whether programmed IO or bus-mastering is used; if a disk controller has the higher priority, it will interrupt a network controller regardless. If I understand you correctly, you want the disk controller only to consume resources when there is no network activity; I'm not too familiar with PCI's or FBSD's arbitration logic, but I assume that FBSD will try to service disk controllers before network controllers (please correct me on this). I'm sure one could change that with some effort to give the nic the higher priority. However, if you're intention is to really make this one router forward packets with lower latency, you might want to try to run it completely off MFS; then there will be no disk activity at all. Stefanhelp
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