[LEAPSECS] Google, Amazon, now Microsoft

Poul-Henning Kamp phk at phk.freebsd.dk
Tue Jun 2 16:25:58 EDT 2015

In message <556D8C59.9040309 at edlmax.com>, Brooks Harris writes:

>> A lot of Windows machines are doing things where you would expect
>> people to care about leap-seconds:  Nuclear power plants control
>> systems, Air Traffic Control computers, Surgery robots, Patient
>> Monitors, Power grid disturbance detectors etc.  etc. etc.

>In many of those uses the PC is not doing the mission critical timing. 
>No event-driven multitasking OS can do precise timing [...]

You're saying this to the bloke who implemented a prototype adaptive
optics solution for the ESO ELT on a plain, unmodified FreeBSD
kernel ?

Anyway, the PC doesn't need to do the RT parts directly in order
to mess them up with wrong timestamps.

>> But this is not something they are happy about doing, much less
>> proud of doing, but weighing the risks of "heterogeneous" leap-second
>> handling and the risk of being up to half a second wrong about time
>> for most of a day, they picked the second risk.
>The failures folks are frightened of are bugs evoked by the Leap Second. 
>At least some of which are just "stupid" bugs, like threading races when 
>outputting the Leap Second event to the system log, not basic 
>timekeeping calculation errors. If all parts of the system did POSIX and 
>NTP correctly the timekeeping would not reflect UTC correctly because 
>neither POSIX or NTP do that anyway, but the systems wouldn't hang or 
>crash. As it is they have to "smear" to minimize the problems.

Which is like saying that if only 50% of all programmers weren't
below the skill-median, we wouldn't have the problem.

Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
phk at FreeBSD.ORG         | TCP/IP since RFC 956
FreeBSD committer       | BSD since 4.3-tahoe    
Never attribute to malice what can adequately be explained by incompetence.

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