i386/104678: SMP not working on Turion XP Laptop

[Ariff Abdullah]

The following reply was made to PR i386/104678; it has been noted by GNATS.

From: Ariff Abdullah <ariff at FreeBSD.org>
To: Bruce Evans <bde at zeta.org.au>
Cc: bug-followup at FreeBSD.org, danolson at visi.com, rainer.alves at gmail.com,
        infofarmer at FreeBSD.org, jhb at FreeBSD.org
Subject: Re: i386/104678: SMP not working on Turion XP Laptop
Date: Fri, 17 Nov 2006 22:50:19 +0800

 On Fri, 17 Nov 2006 23:36:49 +1100 (EST)
 Bruce Evans <bde at zeta.org.au> wrote:
 > On Fri, 17 Nov 2006, Ariff Abdullah wrote:
 > 
 > > It seems the workaround is rather simple:
 > >
 > > machdep.cpu_idle_hlt=0
 > 
 > This sort of works on an HP nx6325 too.  It fixes booting.
 > 
 > > Unfortunately, the only place where you can set that is after the
 > > system comes alive. This patch deals with that so that you can set
 > > it as early as possible during boot procedure through loader.conf.
 > 
 > After booting I had no problems that matter much to me
 > (sleep/suspend don't work; closing the lid only turns off the screen
 > and drops 1 second from the timecounter), but with cpu_idle_hlt=0
 > (set manually in ddb after booting with -d), the system runs very
 > hot, and turning cpu_idle_hlt back on works strangely (it cools an
 > idle system, but stops clock interrupts working), and turning it
 > back off works as expected (it reheats an idle system and restarts
 > clock interrupts). Apparently the SMP hook into cpu_idle() doesn't
 > work right if the flag is changed after booting.
 > 
 > > Summary:
 > > Basically the cpu enter deep sleep mode whenever it receives HLT
 > > call within idle loop, and that only if APIC + Local APIC timer is
 > > enabled. I can't tell whether it is because of APIC misseting, CPU
 > > bug or else, but one thing for sure, FreeBSD 5.x/SMP boots happily
 > > on this (well, that's because it doesn't use local APIC timer).
 > 
 > The boot problem also caused clock interrupts to stop working *until
 > I toggled AC power), so the problem is apparently related to using
 > the local APIC timer.
 > 
 > The power penalty seems to be more than slight.  On my nx6325,
 > tz0.temperature is now 50C with cpu_idle_hlt=1 and 75C with
 > cpu_idle_hlt=0, the latter even when on battery power.  I've also
 > noticed this system getting hot while in ddb, and wondered if it
 > would help to use pause() in the spinloops in console i/o routines.
 > 
 
 Apparently executing HLT on other cores seems fine, as long as we
 _exclude_ at least a single core from doing so. That way, we still
 have manageable timer interrupt while letting the other cores doing
 power management stuffs. Currently, this is my crude crack on
 machdep.c (both for i386 and amd64):
 
 ## BEGIN ##
 void
 cpu_idle(void)
 {
 
 #ifdef SMP
 	if (mp_grab_cpu_hlt())
 		return;
 #endif
 
 	if (cpu_idle_hlt) {
 		disable_intr();
   		if (sched_runnable())
 			enable_intr();
 		else if (PCPU_GET(cpuid) == 0) <<<<<
 			enable_intr();         <<<<<
 		else
 			(*cpu_idle_hook)();
 	}
 }
 ## END ##
 
 
 Again, this only concern where local apic timer is in action for this
 cpu.
 
 
 --
 Ariff Abdullah
 FreeBSD
 
 ... Recording in stereo is obviously too advanced
     and confusing for us idiot ***** users :P ........