cpu stopping

[Mitsuru IWASAKI]

Hi, thanks for comments.

> As the first thing I must admit that I haven't looked at the patch :-)

Never mind :) What I'm trying to do in the patches is just to unify
amd64/i386 independent part (acpi_wakeup.c) for the code maintenance,
so please let's commit it first, then start re-design the
cpususpend_handler().

> But really I don't see why we need to differentiate between stopped and
> suspended state as both of them ultimately mean exactly the same thing - CPUs
> are spinning on some condition (and they are in a well-defined place and state).

Yes, amd64/i386 cpususpend_handler() is very similar to cpustop_handler()
actually, some resume related procedures are added for suspend.

> My view of how this should work is:
> - there can be only one master CPU that controls all other (slave) CPUs
> - the master sets entry and exit hooks

Entry hook for suspending might be
----
                ctx_fpusave(suspfpusave[cpu]);
                wbinvd();
                CPU_SET_ATOMIC(cpu, &stopped_cpus);
----

and for stopping is
----
        /* Indicate that we are stopped */
        CPU_SET_ATOMIC(cpu, &stopped_cpus);
----

Correct?
I think stopping hook can be replaced with suspending hook.


Exit hook for suspending is
----
                pmap_init_pat();
                load_cr3(susppcbs[cpu]->pcb_cr3);
                initializecpu();
                PCPU_SET(switchtime, 0);
                PCPU_SET(switchticks, ticks);
[snip]
        /* Resume MCA and local APIC */
        mca_resume();
        lapic_setup(0);
----

For stopping should be
----
        if (cpu == 0 && cpustop_restartfunc != NULL) {
                cpustop_restartfunc();
                cpustop_restartfunc = NULL;
        }
----

> - the master signals slaves to enter the stop state
> - the slaves execute the enter hook and start spinning on the release condition
> - the master does whatever it wants to do in this special system state
> - the master signals the slaves to resume
> - the slave exit the spin loop and execute the exit hook

I think it would be possible.  However I personally think that
priority of x86/x86/mp_machdep.c is higher and more effective than
merging cpususpend/stop_handler().

Thanks