Re: DECstation 5000/200 timekeeping

[Jonathan Stone <kiwi_jonathan%yahoo.com@localhost>]

 On Sunday, October 31, 2021, 05:27:37 PM PDT, Maciej W. Rozycki <macro%orcam.me.uk@localhost> wrote:

On Sun, 31 Oct 2021, Jonathan Stone wrote:
>> Did you submit a PR for the broken time-keeping?


> Hmm, as it happens we have a timekeeping problem with the VAX port too,
> cf. PR port-vax/56383, so I wonder if this is something generic, perhap
> specific to slower systems which can miss interrupts more easily if we're
> not careful enough in making them delivered in a timely manner.

That doesn't sound plausible. I used to actively develop NTP with Dave Mills and Harlan Stenn, using a DECstation 500/150.
I added cycle-counter support for that, but NTP was quite usable even without. And I regularly used NetBSD on DECstations for networking throughput tests. Also, that 5000/150 has never seen any "sd" SCSI disks since Ralph Campbell's "rz" driver was replaced with the MI "sd" driver. (fails to find a root filesystem, "?" lists nothing)

So I conclude there's some pmax-specific breakage. There may well be sme MI breakage, but the pmax behavior is clearly a regression.
(Mouse's report that pre-1.5 NetBSD has _much_ better timekeeping (their emphasis) seems like good evidence.

I'm not saying there's a single root-cause for both the unacceptable timekeeping, and the SCSI-disk breakage. It's more that I can't test or repro Mouse's report on the machine where I used to build NetBSD releases on, because that newer version of NetBSD never sees any disks on that machine.

Meanwhile: I rescued a Vaxstation-2000 and a Microvax-2000 from dumpster (or possibly eBay) a month or so back, and I just got a Vaxstation-3100 m76 to act as a build server for them. So I guess i'll see :-).