Re: cvs commit: src/sys/conf options.i386 options.pc98 src/sys/i386/conf GENERIC src/sys/i386/i386 machdep.c mp_machdep.c

[David Rhodus <drhodus@xxxxxxxxxxx>]

On Jan 11, 2004, at 12:05 PM, Jeroen Ruigrok/asmodai wrote:

> -On [20040109 22:02], David Rhodus (drhodus@xxxxxxxxxxxxxxxxxxxxxxx) 
> wrote:
> >  	The idea is taken from JHB's changes in FreeBSD but without
> >  	the idle loop changes so as not to get the "Hyerthreading
> >  	slowdown" affect FreeBSD seems to have with HTT.
>
> I have no idea what he did, but from what I gather from various
> resources is that with a lot of idleness you might want to halt the
> respective cores a little bit more than usual to not contend too much
> over the CPU core resources shared by both virtual CPUs.

This has been taken care of already in DragonFly, and a lot easier
because of LWKT already having the per-cpu scheduling we use an IPI
message. Just take a look at the at cpu_idle function inside machdep.c

void
cpu_idle(void)
{
        struct thread *td = curthread;

        crit_exit();
        KKASSERT(td->td_pri < TDPRI_CRIT);
        for (;;) {
                lwkt_switch();

                if (cpu_idle_hlt && !lwkt_runnable() &&
                    (td->td_flags & TDF_IDLE_NOHLT) == 0) {
                        /*
                         * We must guarentee that hlt is exactly the 
instruction
                         * following the sti or we introduce a timing 
window.
                         */
                        __asm __volatile("cli");
                        splz();
                        __asm __volatile("sti; hlt");
                        ++cpu_idle_hltcnt;
                } else {
                        td->td_flags &= ~TDF_IDLE_NOHLT;
                        splz();
                        __asm __volatile("sti");
                        ++cpu_idle_spincnt;
                }
        }
}

With this we when are able to have the scheduler wakeup a target cpu.
So then if a thread wants to run on a particular cpu we just IPI that 
cpu.
This is why the idle loop changes don't apply here anymore, because
we actually have fixed the performance issue with HLT'ing.

-DR