Date: Sun, 17 Feb 2002 15:36:56 -0800 (PST) From: Matthew Dillon <dillon@apollo.backplane.com> To: Michael Smith <msmith@FreeBSD.ORG> Cc: Michael Smith <msmith@FreeBSD.ORG>, Poul-Henning Kamp <phk@critter.freebsd.dk>, Bruce Evans <bde@zeta.org.au>, freebsd-current@FreeBSD.ORG Subject: Re: ACPI timer is screwed... (was Re: 'microuptime() went backwards ...' using ACPI timer. Shouldn't that be impossible? ) Message-ID: <200202172336.g1HNaup07553@apollo.backplane.com> References: <200202172327.g1HNRuA01838@mass.dis.org>
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:Sounds like we need to smack whoever made your chipset as well. Intel
:learned their lesson (finally) with later revisions of the PIIX4. I'm
:guessing you're running this against a ServerWorks system.
atapci0: <ServerWorks ROSB4 ATA33 controller> port 0x8b0-0x8bf at device 15.1 on
pci0
Uh huh.
It might be possible to detect the situation during init-time by
explicitly looking for a reverse indexed time in a tight loop of
maybe a thousand reads, but that would still leave us with a statistical
chance of not guessing right.
:Interesting. This would be reasonably robust in the ripple-counter case
:we have to deal with on the old PIIX4. Have you tried implementing the
:above yet, or measuring how much it costs?
:
:At any rate, please let me know for sure whether you're running on a
:ServerWorks board, and I'll see if I can't find a Big Stick to hit them
:with.
:
:Thanks,
:Mike
I haven't measured the cost (extra loops) but I expect it would stabilize
in no more then one additional loop, which would be three counter reads
total or roughly the same as your originaln _safe code in the worst case.
I think we could default to the _safe version and then explicitly change
it to use the fast version if we see specific chipsets which we know
to be good.
-Matt
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