Date: Wed, 07 Oct 1998 11:26:37 -0700 From: Parag Patel <parag@cgt.com> To: freebsd-smp@FreeBSD.ORG Subject: Re: hw platform Q - what's a good smp choice these days? Message-ID: <199810071826.LAA07841@pinhead.parag.codegen.com> In-Reply-To: Your message of "Wed, 07 Oct 1998 11:10:54 EDT." <19981007111054.39986@amber.org>
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Another point regarding IDE speeds is that the UDMA (33Mb/sec transfer rates) drives can come close to SCSI performance *if* the drivers aren't trying to talk to the PCI-IDE chips in legacy ISA-mode and *if* there is only one master per IDE controller. The BeOS on Intel hardware supports only IDE drives at the moment and has no trouble handling multiple streaming audio and video streams off of a UDMA drive. They were rather pleasantly surprised by the performance. I suspect part of the problem is that FreeBSD's PCI-IDE drivers merely set a few flags and then let the ISA-IDE driver do most of the work in legacy PIO mode. The latest PCI-IDE chips should be entirely programmable using memory-mapped I/O but require all new drivers. One of my back-burner projects is to write an up-to-date driver for PCI-IDE chips to get better performance vs CPU overhead measurements. Another thing to remember with IDE is that you can only talk to one device of a master or slave at a time. To get maximum performance, you should put each IDE device on a separate controller as a master and do not connect anything as a slave on that controller. You definitely don't want to put two hard disks on the same controller. (It's OK to put two relatively slow devices together like CD-ROMs and tape drives which aren't likely to be used simultaneously.) This essentially uses the PCI bus as a connect-disconnect bus to manage multiple transactions to multiple devices, much like the SCSI bus. Another of my projects is to design a PCI plugin board with about 4-6 PCI-IDE chips from CMD and a TI PCI-PCI bridge chip. The idea is to have a whole bunch of IDE plugs to allow having a lot of masters but no slaves. But it's not worth pursuing without a better driver first to see if the performance is acceptable. Heck - it would be the World's Cheapest RAID device using the ccd driver. :-) Of course, I could be completely out to lunch, and I'm sure you folks will tell me. -- Parag To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-smp" in the body of the message
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