Re: high temperature with gnumach and hurd

[Farid Hajji <farid.hajji@ob.kamp.net>]

> > > just wanted to tell you, that the temperature of my cpu is raising to
> > > very high values, while having the hurd system running.
> > > 
> > > If I am working with linux, the temperature of the cpu is somewhere
> > > below 60°C (under heavy load), but if I boot the hurd thing and don't do
> > > anything, the temperature raises to higher 60's and the bios temperature
> > > warning starts howling.
> > 
> > This is intended behaviour: GNU/Hurd is a *hot* OS :-)
> > 
> > > Did anyone else recognize this problem?
> > 
> > Maybe GNUmach should idle/hlt the CPU when all tasks/threads
> > are idle?
> 
>  This was sort of brought up a while ago with respect to a laptop.
> Mach actively sends idle instructions to the cpu, so the cpu is always
> at full usage, this may be causing the heat up.

Exactly. On x86, sending a hlt instruction will block the CPU
until an interrupt trickles in (e.g. hw clock, etc...). 

I don't have GNUmach sources on the box I'm posting from right now,
so here's how it is done on FreeBSD -STABLE:

  /usr/src/sys/i386/i386/machdep.c:

  /*
   * Shutdown the CPU as much as possible
   */
  void
  cpu_halt(void)
  {
          for (;;)
                  __asm__ ("hlt");
  }

  /*
   * Hook to idle the CPU when possible.   This is disabled by default for
   * the SMP case as there is a small window of opportunity whereby a ready
   * process is delayed to the next clock tick.  It should be safe to enable
   * for SMP if power is a concern.
   *
   * On -stable, cpu_idle() is called with interrupts disabled and must
   * return with them enabled.
   */
  #ifdef SMP
  static int      cpu_idle_hlt = 0;
  #else
  static int      cpu_idle_hlt = 1;
  #endif
  SYSCTL_INT(_machdep, OID_AUTO, cpu_idle_hlt, CTLFLAG_RW,
      &cpu_idle_hlt, 0, "Idle loop HLT enable");

  void
  cpu_idle(void)
  {
          if (cpu_idle_hlt) {
                  /*
                   * We must guarentee that hlt is exactly the instruction
                   * following the sti.
                   */
                  __asm __volatile("sti; hlt");
          } else {
                  __asm __volatile("sti");
          }
  }

cpu_halt() and cpu_idle() are called from the scheduler in
/usr/src/sys/i386/i386/swtch.s, but that's off topic here,
so no need to reproduce that code.

Anyone with GNUmach sources available: could you please
post the code of the idle loop? A quick fix for single
CPU systems should be possible and painless, though there
_will_ be issues in the SMP case.

-- 
Farid Hajji. http://www.farid-hajji.net/address.html