can the scheduler decide to schedule an interrupted but runnable thread on another CPU core? What are the implications for code?

[Andrey Chernov]

On 14.02.2014 23:10, John Baldwin wrote:

>> Due to this bug, not fixed yet, the real picture is more complex:
>> http://www.freebsd.org/cgi/query-pr.cgi?pr=kern/163585
> 
> Eh, that bug report has no useful details, as in, it doesn't list the
> actual commands run.  If you do 'cpuset -l 6 -s 1' to force all
> processes to only use CPU6, then yes, of course the other CPUs are idle
> because that's what you _asked_ for.  AFAICT, that is all the original
> reporter did.  At work we regularly add and remove CPUs from the
> default set (set 1) on hundreds of machines every day with ULE without
> any issues.

Probably original report lack certain commands, but I provide the link
to the port which reproduces this bug too. All threads there are
assigned to the _different_ CPUs and appears as result on single one
with SCHED_ULE (not with SCHED_4BSD). And it is what original reporter
mean too. It surely happens, maybe not the first time, but on 2nd-3rd.
It means that cpuset_setaffinity() is completely broken form SCHED_ULE
at least for 3 years.

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