Date: Fri, 30 May 2014 20:49:51 -0600 From: Ian Lepore <ian@FreeBSD.org> To: Fred Pedrisa <fredhps10@hotmail.com> Cc: 'freebsd-current' <freebsd-current@FreeBSD.org> Subject: Re: Thread Scheduler Priority Message-ID: <1401504591.20883.28.camel@revolution.hippie.lan> In-Reply-To: <COL131-DS40CDAE671F4A6060C9A85B0240@phx.gbl> References: <COL131-DS40CDAE671F4A6060C9A85B0240@phx.gbl>
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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, ¶m[gnThreadID]) != 0)
>
> {
>
> error
> ("Unable to get priority");
>
> return 1;
>
> }
>
>
> param[gnThreadID].sched_priority = 99;
>
> if
> (pthread_setschedparam(ts[gnThreadID], police, ¶m[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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