Date: Thu, 2 Jul 2009 10:21:55 -0400 From: Larry Baird <lab@gta.com> To: Paul Thornton <prt@prt.org> Cc: freebsd-net@freebsd.org Subject: Re: Polling and kern.polling.idle_poll Message-ID: <20090702142155.GA71817@gta.com> In-Reply-To: <4A4C9FCC.6020304@prt.org> References: <20090630180029.GA8847@gta.com> <4A4C9FCC.6020304@prt.org>
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Paul,
> Larry Baird wrote:
> >The man page for polling states:
> > kern.polling.idle_poll
> > Controls if polling is enabled in the idle loop. There are no
> > reasons (other than power saving or bugs in the scheduler's han-
> > dling of idle priority kernel threads) to disable this.
> >
> >So why is it now disabled by default? Looking back through cvs the
> >change was made by Luigi way back in August of 2002.
> >
> >
> Did you ever get a reply for this question on the -net list? I may have
> missed it, but I don't think you did.
> I'm very interested in why this was changed too.
I got some off list mail from Luigi. In 4.x, the idle_poll() was called
from idle. Now it is its own thread. CPU statistics will now show high 100%
utilization if your set kern.polling.idle_poll. He also has some concerns
about if locking was in place for SMP. Looking at the code locking appears
to be in place.
The performance improvment is too great for me to ignore, so I made a few
mods to my kernels. I modified kern_poll to set P_NOLOAD for the idle_poll
thread. I then modified CPU statistics to view all processes with P_NOLOAD
as the idle process. So far working great for me. Patches below.
*** /sys/kern/kern_poll.c 2006-06-16 18:11:55.000000000 -0400
--- kern_poll.c 2009-07-02 10:03:07.000000000 -0400
***************
*** 577,583 ****
--- 577,587 ----
{
struct thread *td = curthread;
struct rtprio rtp;
+ struct proc *p = td->td_proc;
+ PROC_LOCK(p);
+ p->p_flag |= P_NOLOAD;
+ PROC_UNLOCK(p);
rtp.prio = RTP_PRIO_MAX; /* lowest priority */
rtp.type = RTP_PRIO_IDLE;
mtx_lock_spin(&sched_lock);
*** /sys/kern/kern_clock.c 2008-06-04 06:31:41.000000000 -0400
--- kern_clock.c 2009-07-02 10:05:01.000000000 -0400
***************
*** 516,522 ****
thread_statclock(0);
td->td_sticks++;
p->p_rux.rux_sticks++;
! if (td != PCPU_GET(idlethread)) {
cp_time[CP_SYS]++;
pcp_time[CP_SYS]++;
} else {
--- 516,522 ----
thread_statclock(0);
td->td_sticks++;
p->p_rux.rux_sticks++;
! if ( ! (p->p_flag & P_NOLOAD) ) {
cp_time[CP_SYS]++;
pcp_time[CP_SYS]++;
} else {
--
------------------------------------------------------------------------
Larry Baird | http://www.gta.com
Global Technology Associates, Inc. | Orlando, FL
Email: lab@gta.com | TEL 407-380-0220, FAX 407-380-6080
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