On Thu, 2014-05-29 at 02:12 -0300, Fred Pedrisa wrote:
Hi, Guys.
How can I adjust a certain thread to have the maximum system priority in the
scheduler ?
I've tried doing it this way :
/* Set thread priority. */
if
(pthread_getschedparam(ts[gnThreadID], police, param[gnThreadID]) != 0)
{
error
(Unable to get priority);
return 1;
}
param[gnThreadID].sched_priority = 99;
if
(pthread_setschedparam(ts[gnThreadID], police, param[gnThreadID]) != 0)
{
error(Unable to set priority);
return 1;
}
However, in 'top', I don't see the process threads switching to -92
priority, like other threads in the system, is something I did wrong or
maybe I might be missing something ?
You can't just set the priority to any number you want... per the man
page for pthread_setschedparam() the value has to fall within the ranges
returned by sched_get_priority_min() and sched_get_priority_max() for
the given scheduling class. On freebsd those ranges are 0-31.
I suspect from your statement of wanting maximum system priority maybe
what you need to do is change the scheduling class from SCHED_OTHER to
SCHED_RR, that should give you realtime priority. Be aware that a
realtime thread that is compute-bound will take over the system (or one
core on an SMP system); it will get all cycles if it is always runnable.
If what you're looking for is the thread equivelent of using the nice
command, so that you give a boost to a thread over other threads in the
timeshare (SCHED_OTHER) scheduling class, there is currently no way to
do that in freebsd.
Last year for $work I about went crazy trying to figure out the mapping
between pthread scheduling classes and priorities and freebsd's idea of
thread prorities. I eventually gave up on the pthread API and used the
freebsd native function rtprio_thread() instead.
-- Ian
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