[LEAPSECS] Google, Amazon, now Microsoft

[Brooks Harris]

On 2015-06-03 10:55 AM, Poul-Henning Kamp wrote:
> --------
>
> In message <556F0C92.4020509 at edlmax.com>, Brooks Harris writes:
>
>>> You're saying this to the bloke who implemented a prototype adaptive
>>> optics solution for the ESO ELT on a plain, unmodified FreeBSD
>>> kernel ?
>> I didn't know that, very impressive. Is there information anywhere how
>> it was done?
> I did a presentation at a workshop at ESO in december 2012, the
> slides seems to be here:
>
>          https://www.eso.org/sci/meetings/2012/RTCWorkshop/proceedings.html
>
Oh great! On quick glance that's just the sort of RT discussion I was 
interested in. I'll study it more.
> I'm not sure what the legal status is for deeper info.  You'd have
> to ask them for access.  The person to talk to is Nick Kornweibel.
And dig deeper when I can.
>> I bring the RT aspect [...]
> The first point here is that commodity *NIX, be it LINUX, FreeBSD
> or something else is often used to pull time into systems, even
> if they themselves don't do the RT part.
Yes, right, as I said, if not so clearly, "some sort of hardware 
assist". In my land we have things like SDI, perhaps on PCI, feeding 
video/audio in "real-time", or "device control" (remote control of 
video/audio devices) protocols that arrive at serial ports (COM or USB 
or something) in "real-time". Those sources often have high quality 
oscillators and timebases and the protocols support deterministic 
delivery to the port. You then have to carefully interface through 
worker threads and buffers to hang the timestamps on the video/audio 
samples, etc. That can be tricky, and often involving the manufacture's 
NT device drivers (some work better than others!), or you may need to 
build a driver yourself, notoriously tricky, but down there you can get 
really close to the metal (ring 0) if you're careful. But its never an RTOS.

>
> The other thing to notice is that even if it is not RT in the strict
> classical sense, commodity *NIX does things which matter on
> microsecond resolution timescales.  (As for instance the ESO thing).
Right. Thanks,

>
>> The time on Microsoft Azure will be Different by a second, everywhere
>> http://www.theregister.co.uk/2015/05/29/windows_azure_second_out_of_sync/
>>
>> As I said earlier - A) Where did they get this information? B) Is it
>> true? C) Is that how Windows is behaving?
> A) Ask them.
Can try.
> (M$ probably notified their customers ?)
They did -

How the Windows Time service treats a leap second
https://support.microsoft.com/en-us/kb/909614

>
> B) I have no reason to doubt it.  The Reg is usually very good on truth.
I doubt it now -

"Contrary to one post I recently read, Microsoft doesn’t implement a 
leap second time zone by time zone – in other words, in a rolling 
fashion, like the way we watch new year celebrations count down around 
the world. Essentially, the leap second occurs at the same time 
everywhere."

Another look at the impact of the coming 2015 leap second (not much)
http://blogs.msdn.com/b/mthree/archive/2015/06/01/2015-leap-second-060115.aspx 


Also How the Windows Time Service Works
https://technet.microsoft.com/en-us/library/cc773013(v=ws.10).aspx

>
> C) Probably only in Azure.
As above, I doubt it.
> Other Windows will probably do the
>     usual Windows thing:  Step a second some time later.
Yes. It looks like it can be kept pretty close with a careful use of 
Windows Time Service, but thats not usually active on typical machines.

Leap Seconds are not the only thing might upset the apple cart -

Summary of Windows Azure Service Disruption on Feb 29th, 2012
http://azure.microsoft.com/blog/2012/03/09/summary-of-windows-azure-service-disruption-on-feb-29th-2012/

-Brooks
>