Rob wrote:
Martin Burnicki <martin.burni...@meinberg.de> wrote:
Except what I've mentioned before I have had rare cases where the
Windows timekeeping was generally broken due to some drivers.
If I remember correctly then one case was a hard disk driver, and a some
latency checker program was used to show that the driver had blocked
IRQs for too long, so the timekeeping was strongly degraded.
There have been early IDE disks, 20 years ago, that required the entire
transfer of a block to occur without interruption. The drivers for those
disks disabled interrupts during the transfer.
This happened on Linux as well. You could set a flag not to do this,
on your own risk, and you would start to see corrupted blocks.
Of course, later the disk transfers happened under DMA and probably
the braindead disk firmware was fixed as well.
Yes, I know those problems dated 20 years ago.
However, both cases I've mentioned occurred in 2012 under Windows Server
2008 R2 and Windows 7 x64.
When searching for details I found this discussion here where another
user had similar problems caused by a serial card driver:
http://lists.ntp.org/pipermail/questions/2012-January/031744.html
The cases I meant originally were with Windows Server 2008 R2, where a
specific version of the Nvidia display driver caused such effects, and
also with Windows 7 x64, where a user ran some DPC latency checkers
which found out that the ataport.sys driver shipped with Windows caused
latency peaks of up to 4 ms, occurring every 3s.
Those cases were not discussed in the NG but via email with Meinberg
customers.
We may have to keep in mind, though, that at the time back in 2012 when
the cases were discussed bug 2328 (time adjustments of less than 16 are
ignored by Windows)
https://bugs.ntp.org/show_bug.cgi?id=2328
had not been reported, and thus no workaround was in ntp-dev at that
time, so you can't tell if that would have improved the timekeeping in
these cases.
Martin
--
Martin Burnicki
Meinberg Funkuhren
Bad Pyrmont
Germany
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