From owner-freebsd-current  Tue Dec 18 16: 9:53 2001
Delivered-To: freebsd-current@freebsd.org
Received: from iguana.aciri.org (iguana.aciri.org [192.150.187.36])
	by hub.freebsd.org (Postfix) with ESMTP
	id A981E37B417; Tue, 18 Dec 2001 16:09:49 -0800 (PST)
Received: (from rizzo@localhost)
	by iguana.aciri.org (8.11.3/8.11.1) id fBJ09nf90278;
	Tue, 18 Dec 2001 16:09:49 -0800 (PST)
	(envelope-from rizzo)
Date: Tue, 18 Dec 2001 16:09:49 -0800
From: Luigi Rizzo <rizzo@aciri.org>
To: current@freebsd.org
Cc: peter@freebsd.org
Subject: vm_zeropage priority problems.
Message-ID: <20011218160949.B89864@iguana.aciri.org>
Mime-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
User-Agent: Mutt/1.3.23i
Sender: owner-freebsd-current@FreeBSD.ORG
Precedence: bulk
List-ID: <freebsd-current.FreeBSD.ORG>
List-Archive: <http://docs.freebsd.org/mail/> (Web Archive)
List-Help: <mailto:majordomo@FreeBSD.ORG?subject=help> (List Instructions)
List-Subscribe: <mailto:majordomo@FreeBSD.ORG?subject=subscribe%20freebsd-current>
List-Unsubscribe: <mailto:majordomo@FreeBSD.ORG?subject=unsubscribe%20freebsd-current>
X-Loop: FreeBSD.ORG

[Cc peter because he introduced this code]

Hi,
i was trying the following code in -current (basically copied from
vm_zeropage.c), to implement device polling in the idle loop, and
noticed that the process would take all of the CPU time. Being
suspicious that something was wrong with priorities, I added a
couple of printfs, and to my surprise, the priority of the process
(pri_level) after the first tsleep() becomes 104 instead of staying
at 255 as it was originally initialized.

A quick scan of the files in sys/sys shows that 104 is PPAUSE,
and this is the source of the problem.

I guess this is a bug in vm_zeropage.c, the second parameter
in tsleep should be td->td_ksegrp->kg_pri.pri_level instead
of PPAUSE, or at least the priority should be reset to the
original value after returning from the tsleep ?

	cheers
	luigi

static void
poll_idle(void)
{
        struct thread *td = curthread;
        struct rtprio rtp;
 
        rtp.prio = RTP_PRIO_MAX;        /* lowest priority */
        rtp.type = RTP_PRIO_IDLE;
        mtx_lock_spin(&sched_lock);
        rtp_to_pri(&rtp, &td->td_ksegrp->kg_pri);
        mtx_unlock_spin(&sched_lock);
   
        printf("idlepoll start and sleep, pri is %d native %d user %d\n",
                td->td_ksegrp->kg_pri.pri_level,
                td->td_ksegrp->kg_pri.pri_native,
                td->td_ksegrp->kg_pri.pri_user);
        for (;;) {
                if (poll_in_idle && poll_handlers > 0) {
                        idlepoll_sleeping = 0;
                        mtx_lock(&Giant);
                        ether_poll(poll_each_burst);
                        mtx_unlock(&Giant);
                        mtx_assert(&Giant, MA_NOTOWNED);
                        mtx_lock_spin(&sched_lock);
                        setrunqueue(td);
                        td->td_proc->p_stats->p_ru.ru_nvcsw++;
                        mi_switch();
                        mtx_unlock_spin(&sched_lock);
                } else {
			printf("idlepoll goes to sleep, "
				"pri is %d native %d user %d\n",
				td->td_ksegrp->kg_pri.pri_level,
				td->td_ksegrp->kg_pri.pri_native,
				td->td_ksegrp->kg_pri.pri_user);
                        idlepoll_sleeping = 1;
                        tsleep(&idlepoll_sleeping, PPAUSE, "pollid", hz * 3);
                }
        }
}

static struct proc *idlepoll;
static struct kproc_desc idlepoll_kp = {
         "idlepoll",
         poll_idle,
         &idlepoll
};
SYSINIT(idlepoll, SI_SUB_KTHREAD_VM, SI_ORDER_ANY, kproc_start, &idlepoll_kp)


To Unsubscribe: send mail to majordomo@FreeBSD.org
with "unsubscribe freebsd-current" in the body of the message