[haiku-appserver] Re: CPU-idle-loop and HALT instruction?
- From: Ingo Weinhold <bonefish@xxxxxxxxxxxxxxx>
- To: haiku-appserver@xxxxxxxxxxxxx
- Date: Tue, 13 Dec 2005 00:46:51 +0100
On 2005-12-13 at 00:33:10 [+0100], Stephan Assmus <superstippi@xxxxxx> wrote:
> On 2005-12-13 at 00:26:58 [+0100], Ingo Weinhold <bonefish@xxxxxxxxxxxxxxx>
> wrote:
> > On 2005-12-12 at 23:52:06 [+0100], Stephan Assmus <superstippi@xxxxxx>
> > wrote:
> > > > > Or, is it already in there and can I somehow enable it?
> > > >
> > > > From src/system/kernel/arch/x86/arch_cpu.c:
> > > >
> > > > void
> > > > arch_cpu_idle(void)
> > > > {
> > > > switch (smp_get_num_cpus()) {
> > > > case 0:
> > > > panic("You need at least 1 CPU to run Haiku\n");
> > > > case 1:
> > > > asm("hlt");
> > > > default:
> > > > break;
> > > > }
> > > > }
> > > >
> > > > So, if you have more than one CPU, the only thing you can do is change
> > > > this
> > > > code. There might be a reason, why it is implemented like it is,
> > > > though.
> > > > On
> > > > the other hand there's also no comment that you computer will explode
> > > > when
> > > > executing "hlt" on a multi CPU machine either...
> > >
> > > I seem to recall that on my dual CPU machine, there is simply two idle
> > > threads running. Or is my memory failing me?
> >
> > No. The question was, what the idle threads are executing, though. And
> > that's
> > the above function (in an endless loop).
>
> Yeah, but why would a person with more than one CPU have to change that
> code,
> if the real fix is making sure that there is simply as many idle threads as
> CPUs? (Somewhere else form this code.) Or am I totally confused?
Yep, you're totally confused. ;-)
There are as many idle threads as there are CPUs. Each of which executing the
above function in a endless loop. The real fix is to change the above code to
also execute "hlt" when there's more than one CPU. The only suspicious thing
is why this hadn't been done in the first place.
CU, Ingo
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