sched_ule performance on single CPU

[Oliver Fromme]

Sorry for the late reply, but I think there's a technical
detail that should be mentioned ...

Unga <unga888 at yahoo.com> wrote:
 > My earlier test shows processes in the normal category
 > can starve processes in real-time category. That's
 > alarming. It should be get fixed.

Note that FreeBSD does not support "hard real time"
processing.  Strictly speaking no OS does that on PC
standard hardware.

FreeBSD's idprio/rtprio implementation only affects
the decisions of the scheduler, i.e. the assignment
of CPU time slices to processes.  However, there are
other resources beside CPU that influence the execution
of processes.  For example disk I/O.

In other words, if an idle-prio process performs a lot
of disk accesses, it creates an I/O bottleneck, and
even realtime-prio processes will have to wait because
the hardware (disk) is blocked.  This problem can be
alleviated by using faster and better hardware, e.g.
a SCSI RAID-0 disk subsystem or whatever.  Besides,
for professional audio recording you will also need
professional audio hardware (which should include its
own buffer memory, among other things), not a consumer
card or an el'cheapo USB dongle.

Best regards
   Oliver

PS:  My notebook at home (Pentium-M, UP, 3 years old)
works very well with FreeBSD/i386 RELENG_7 + SCHED_ULE.

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Oliver Fromme, secnetix GmbH & Co. KG, Marktplatz 29, 85567 Grafing b. M.
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