Priority scheduling in 6.x

Pramod Srinivasan pramod at
Thu Jan 15 14:21:42 PST 2009

Hi Daniel

Thanks for your response.

On 1/14/09 7:25 PM, "Daniel Eischen" <deischen at> wrote:

> On Wed, 14 Jan 2009, Pramod Srinivasan wrote:
>> Hi,
>> I have 3 threads low, medium and high , and the scheduling policy is set to
>> SCHED_FIFO. The priority of the threads are at 28,29,30 respectively. Looks
>> like on FreeBSD 6.x, the priority of the threads are not honored while
>> scheduling the threads, but the same test on FreeBSD 7.x seems to work fine.
>> Are there known issues with the priority scheduling in FreeBSD 6.x or am I
>> doing something wrong? (I am using libthr)
> Are you using libpthread or libthr on 6.3?

I am using libthr on 6.1, but had similar issues on 6.2 as well.

> If you are using libthr, then you need to be running with
> superuser privileges for SCHED_FIFO to work.  I'm not sure
> if this works correctly at all in 6.3.

I am running the program with super user privileges on 6.1, tried this on
6.2 as well. Priority scheduling using libthr does not work, unless I am
missing something very basic?. The same program works fine on 7.1, any

> If you are using libpthread, then it will work if the
> threads are PTHREAD_SCOPE_PROCESS, but will not work
> if they are PTHREAD_SCOPE_SYSTEM.  You do not need
> superuser privileges for SCHED_FIFO with libpthread
> and process scope threads.  I don't believe the kernel
> has ever worked properly for libpthread (kse) SCHED_FIFO
> system scope threads.
I tried libpthread with PTHREAD_SCOPE_PROCESS, it was better, I see that the
priority is honored. Thanks for the pointer.


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