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SubjectRe: [BUG] sched_setattr() SCHED_DEADLINE hangs system
On 05/11/2014 04:54 PM, Michael Kerrisk (man-pages) wrote:
> [Dave: I wonder if there's anything trinity can add in the way of
> a test here?]
>
> Hi Peter,
>
> This looks like another bug in sched_setattr(). Using the program
> below (which you might find generally helpful for testing), I'm
> able to reliably freeze up my x64 (Intel Core i7-3520M Processor)
> system for up to about a minute when I run with the following
> command line:
>
> $ time sudo ./t_sched_setattr d 18446744072 18446744072 18446744073
>
> 'd' here means use SCHED_DEADLINE, then the remaining arguments
> are the Runtime, Deadline, and Period, expressed in *seconds*.
> (Those number by the way are just a little below 2^64.)
>
> Aside from interpreting its command-line arguments, all that the
> program does is call sched_setattr() and displays elapsed times.
> (By the way, on my system I see some weird effects for time(2),
> presumably VDSO effects.)
>
> Here's sample run:
>
> time sudo ./t_sched_setattr d 18446744072 18446744072 18446744073
> Runtime = 18446744072000000000
> Deadline = 18446744072000000000
> Period = 18446744073000000000
> About to call sched_setattr()
> Successful return from sched_setattr() [6 seconds]
>
> real 0m40.421s
> user 0m3.097s
> sys 0m30.804s
>
> After unfreezing the machine is fine, while the program is running,
> the machine is pretty unresponsive.
>
> I'm on kernel 3.15-rc4.

Hi Peter,

I realize my speculation was completely off the mark. time(2) really
is reporting the truth, and the sched_setattr() call returns immediately.
But it looks like with these settings the deadline scheduler gets itself
into a confused state. The process chews up a vast amount of CPU time
for the few actions (including process teardown) that occur after
the sched_setattr() call, and since the SCHED_DEADLINE process has
priority over everything else, the system locks up.

Cheers,

Michael


--
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/


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