From owner-freebsd-hackers  Wed May 13 11:41:42 1998
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From: John Hay <jhay@mikom.csir.co.za>
Message-Id: <199805131841.UAA10458@zibbi.mikom.csir.co.za>
Subject: sched_setscheduler() usage?
To: hackers@FreeBSD.ORG
Date: Wed, 13 May 1998 20:41:28 +0200 (SAT)
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Hi,

The latest versions of ntp4 detects that we have sched_setscheduler(2)
and try to use it with this piece of code:

-------------------
# if defined(HAVE_SCHED_SETSCHEDULER)
        {
                struct sched_param sched;

                sched.sched_priority = sched_get_priority_min(SCHED_FIFO);
                if ( sched_setscheduler(0, SCHED_FIFO, &sched) == -1 )
                {
                        msyslog(LOG_ERR, "sched_setscheduler(): %m");
                }
        }
# else /* not HAVE_SCHED_SETSCHEDULER */
-------------------

The problem is that this seems to give ntpd a lower priority (something
like idle priority) because any normal priority program that is cpu
intensive will starve ntpd totally.

So should this piece of code result in higher priority than normal
programs (like the rtprio stuff) or is this piece of code broken? I
assume the ntp guys wanted ntpd to be scheduled at a relatively
high priority to keep delays and jitter to a minimum.

Another question, where does the sched_setscheduler() priorities fit
in with the rest of our priorities? I have started to look through
the kernel code, but because I don't know what its relationship to
the rest of the priorities should be, it is difficult to figure out
where the problem is.

John
-- 
John Hay -- John.Hay@mikom.csir.co.za

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