2015-04-06 17:45-0600, James Sullivan:
> Currently, apic_get_arb_pri() is unimplemented and returns 0.
>
> Implemented apic_get_arb_pri() and added two helper functions
> apic_compare_prio() and apic_lowest_prio() to be used for LAPIC
> arbitration.
>
> Signed-off-by: James Sullivan <sullivan.jame...@gmail.com>
> ---
> +static int apic_compare_prio(struct APICCommonState *cpu1,
> + struct APICCommonState *cpu2)
> +{
> + return apic_get_arb_pri(cpu1) - apic_get_arb_pri(cpu2);
> +}
> +
> +static struct APICCommonState *apic_lowest_prio(const uint32_t
> + *deliver_bitmask)
> +{
> + APICCommonState *lowest = NULL;
> + int i, d;
> +
> + for (i = 0; i < MAX_APIC_WORDS; i++) {
> + if (deliver_bitmask[i]) {
> + d = i * 32 + apic_ffs_bit(deliver_bitmask[i]);
> + if (!lowest || apic_compare_prio(local_apics[d], lowest) < 0) {
> + lowest = local_apics[d];
deliver_bitmask is 8 times u32 to express all 255 possible APICs.
apic_ffs_bit() takes the last set bit, so this loop incorrectly
considers only up to 8 candidates for lowest priority delivery.
foreach_apic() could be used when fixing it, which would also avoid a
'local_apic[d] == NULL' crash.
> + }
> + }
> + }
> + return lowest;
(For consideration:
APM 2-16.2.2 Lowest Priority Messages and Arbitration
If there is a tie for lowest priority, the local APIC with the highest
APIC ID is selected.
Intel is undefined in spec and picks the lowest APIC ID in practice.)
> @@ -336,8 +360,27 @@ static int apic_get_ppr(APICCommonState *s)
>
> static int apic_get_arb_pri(APICCommonState *s)
(I'd call it apic_get_apr() -- we return the state of that register.)
> {
> - /* XXX: arbitration */
> - return 0;
> + int tpr, isrv, irrv, apr;
> +
> + tpr = apic_get_tpr(s);
> + isrv = get_highest_priority_int(s->isr);
> + if (isrv < 0) {
> + isrv = 0;
> + }
> + isrv >>= 4;
> + irrv = get_highest_priority_int(s->irr);
> + if (irrv < 0) {
> + irrv = 0;
> + }
> + irrv >>= 4;
> +
> + if ((tpr >= irrv) && (tpr > isrv)) {
> + apr = s->tpr & 0xff;
> + } else {
> + apr = ((tpr & isrv) > irrv) ? (tpr & isrv) : irrv;
> + apr <<= 4;
> + }
> + return apr;
> }
(This function is called too much IMO.
The trivial optimization is to memorize apic_get_arb_pri() of lowest
priority LAPIC. And you can instantly return if it is 0.
The more complicated one is to use ARB as a real LAPIC register and
update it on TPR/ISR/IRR change, so apic_get_arb_pri() would be just
'return s->apr;'.)
