Re: ATA driver and the clock

[Michael <macallan%netbsd.org@localhost>]

Hello,

On Mon, 17 Jun 2013 09:41:23 +0200
Manuel Bouyer <bouyer%antioche.eu.org@localhost> wrote:

> On Sun, Jun 16, 2013 at 09:22:41PM -0500, Donald Lee wrote:
> > I had a problem this last couple of days where I was seeing the HW clock run
> > backwards, only under heavy (and only particular types of) disk load.
> > 
> > I was seeing this sort of thing in the log:
> > 
> > Jun 15 20:48:41 charm mdnsd: mDNSPlatformRawTime went backwards by 275 
> > ticks; se
> > tting correction factor to 1462875659
> > Jun 15 20:49:18 charm mdnsd: mDNSPlatformRawTime went backwards by 503 
> > ticks; se
> > tting correction factor to 1462876162
> > Jun 15 20:49:24 charm mdnsd: mDNSPlatformRawTime went backwards by 350 
> > ticks; se
> > tting correction factor to 1462876512
> > Jun 15 20:50:41 charm mdnsd: mDNSPlatformRawTime went backwards by 438 
> > ticks; se
> > tting correction factor to 1462876950
> > Jun 15 20:52:33 charm /netbsd: wdc0:0:0: lost interrupt
> > Jun 15 20:52:33 charm /netbsd:  type: ata tc_bcount: 16384 tc_skip: 0
> > Jun 15 20:52:33 charm /netbsd: wdc0:0:0: lost interrupt
> > Jun 15 20:52:33 charm /netbsd:  type: ata tc_bcount: 2048 tc_skip: 0
> > Jun 15 20:52:47 charm /netbsd: wdc0:0:0: lost interrupt
> > Jun 15 20:52:47 charm /netbsd:  type: ata tc_bcount: 16384 tc_skip: 0
> > Jun 15 20:52:48 charm mdnsd: mDNSPlatformRawTime went backwards by 315 
> > ticks; se
> > tting correction factor to 1462877265
> > Jun 15 20:53:29 charm mdnsd: mDNSPlatformRawTime went backwards by 179 
> > ticks; se
> > tting correction factor to 1462877444

> > I also could run "top -s 1" and see the clock "stop" while the disk
> > load was active.  When the activity stopped, the clock would resume.
> > 
> > I was afraid this was HW, and it was - the ATA cable.
> > 
> > I swapped out the cable, and now the problem is (almost?)
> > gone.

Is this a Heathrow-based box?
My beige G3 wouldn't run with DMA enabled until I switched out all the
IDE cables. I thought this was a driver bug and DMA was just hosed on
Heathrow...

> > Me thinks that a bad cable should cause disk errors, and maybe
> 
> You have a "disk error" in the log you posted above: the lost interrupt.
> The disk is not at fault, it's a communication issue between the disk and
> controller. And the driver manager to recover from this situation
> (but you're luky :)
> 
> > delays, but mess up the clock and make it run backwards?
> > Not so much.
> > 
> > The ATA (wd) driver must be turning off interrupts in some brutal
> > way, and then wandering off to handle (long duration)
> > errors.
> 
> It does; the disk reset to recover from this situation can be using
> delay(9). Maybe it could be done in some other way, but I think it's wouldn't
> be a good thing to add complexity in this code (as there's basically no
> way to test it on demand) to "fix" a rare problem which, really,
> needs to be fixed at the hardware level anyway.

I can reproduce this on demand. Kinda. My beige G3 does this on every
boot - whines about a lost interrupt, pauses for a bit, recovers and
then keeps going normally, without further errors.

have fun
Michael