Date: Sun, 5 Jan 2003 23:04:48 -0500 From: "Adam Maas" <mykroft@explosive.mail.net> To: "Bruce Campbell" <bruce@engmail.uwaterloo.ca>, <freebsd-hardware@FreeBSD.ORG> Cc: <freebsd-questions@FreeBSD.ORG> Subject: Re: ata "fallback to PIO mode" on dual processor AMD systems Message-ID: <001e01c2b538$c1375460$7419cdcd@ticking> References: <1041368236.3e1204ac45da5@www.nexusmail.uwaterloo.ca> <025701c2b112$ddfbf580$1200a8c0@gsicomp.on.ca> <1041371397.3e121105cdf30@www.nexusmail.uwaterloo.ca> <1041822086.3e18f1868e32c@www.nexusmail.uwaterloo.ca>
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This would be legacy behaviour from the days of buggy ATA33/UDMA implementations, where falling back to PIO mode would allow a device with a buggy UDMA implementation (Unfortunately rather common at the time) to function. --Adam ----- Original Message ----- From: "Bruce Campbell" <bruce@engmail.uwaterloo.ca> To: <freebsd-hardware@FreeBSD.ORG> Cc: <freebsd-questions@FreeBSD.ORG> Sent: Sunday, January 05, 2003 10:01 PM Subject: Re: ata "fallback to PIO mode" on dual processor AMD systems > Quoting Bruce Campbell <bruce@engmail.uwaterloo.ca>: > > > Quoting Matthew Emmerton <matt@gsicomp.on.ca>: > > > > > [ cc'ing Soren since he's the ATA guru ] > > > > > > > Dec 30 23:27:00 ecserv13 /kernel: ad0: trying fallback to PIO mode > > > > Dec 30 23:27:00 ecserv13 /kernel: ata0: resetting devices .. done > > > > > > > > The test continues to run with the ata controller in PIO mode, with > > > > slower performance, and higher load average. > > > > > > > > Once the master drops to PIO, attempts to access the slave then cause > > > > it to drop to PIO. > > > > > > Are you using 80-conductor cables on all your drives? These are required > > to > > > get consistent high throughput, and running without them may cause the > > > problems you're seeing. > > > > Thanks for the information about the design of IDE etc, and the suggestion > > about the cables. I was about to shuffle things to get the disks > > onto separate channels, but I now see that would be a mistake as my > > CD drive would share a cable with a disk. > > ps. As an aside, I have since determined that putting a PIO device and > a UDMA device on the same channel does not affect the performance > of the UDMA device, unless the PIO device is in use. So, sharing > a low use CD rom drive with a disk wouldn't be so bad. > > I am puzzled about the fallback to PIO concept. If a disk has > gives some sort of timeout error or whatever, why would trying > PIO correct the problem ? That seems equivalent to asking the > disk to do the same thing, just more slowly. > > In my case, some sort of timeout error occurs on ad0, so > it falls back to PIO, and works. A later access to ad1 > also yields a timeout error, and then it drops to PIO, > and works too. I'm fairly confident both disks did not > experience media errors at the same time, which suggests > a problem with the onboard IDE controller, or a driver bug. > > Tests continue... > > > > > > > > ---------------------------------------- > This mail sent through www.mywaterloo.ca > > To Unsubscribe: send mail to majordomo@FreeBSD.org > with "unsubscribe freebsd-questions" in the body of the message > To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-questions" in the body of the message
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