[Qemu-devel] Re: [PATCH v3 3/3] piix_pci: optimize set irq path

["Michael S. Tsirkin" <mst@redhat.com>]

On Tue, Mar 22, 2011 at 11:07:03PM +0900, Isaku Yamahata wrote:
> On Tue, Mar 22, 2011 at 03:40:16PM +0200, Michael S. Tsirkin wrote:
> > On Tue, Mar 22, 2011 at 09:50:37AM +0900, Isaku Yamahata wrote:
> > > On Mon, Mar 21, 2011 at 04:10:22PM +0200, Michael S. Tsirkin wrote:
> > > > > @@ -37,8 +37,27 @@
> > > > >  
> > > > >  typedef PCIHostState I440FXState;
> > > > >  
> > > > > +#define PIIX_NUM_PIC_IRQS       16      /* i8259 * 2 */
> > > > > +#define PIIX_NUM_PIRQS          4ULL    /* PIRQ[A-D] */
> > > > 
> > > > I've changed this to
> > > > ((uint64_t)PCI_NUM_PINS)
> > > > 
> > > > Makes sense?
> > > 
> > > No. The number of pirq is independent of PCI_NUM_PINS.
> > 
> > OK, here's what confuses me:
> > 
> > > diff --git a/hw/piix_pci.c b/hw/piix_pci.c
> > > index e88df43..f07e19d 100644
> > > --- a/hw/piix_pci.c
> > > +++ b/hw/piix_pci.c
> > > @@ -37,8 +37,27 @@
> > >  
> > >  typedef PCIHostState I440FXState;
> > >  
> > > +#define PIIX_NUM_PIC_IRQS       16      /* i8259 * 2 */
> > > +#define PIIX_NUM_PIRQS          4ULL    /* PIRQ[A-D] */
> > > +#define PIIX_PIRQC              0x60
> > > +
> > >  typedef struct PIIX3State {
> > >      PCIDevice dev;
> > > +
> > > +    /*
> > > +     * bitmap to track pic levels.
> > > +     * The pic level is the logical OR of all the PCI irqs mapped to it
> > > +     * So one PIC level is tracked by PIIX_NUM_PIRQS bits.
> > > +     *
> > > +     * PIRQ is mapped to PIC pins, we track it by
> > > +     * PIIX_NUM_PIRQS * PIIX_NUM_PIC_IRQS = 64 bits with
> > > +     * pic_irq * PIIX_NUM_PIRQS + pirq
> > > +     */
> > > +#if PIIX_NUM_PIC_IRQS * PIIX_NUM_PIRQS > 64
> > > +#error "unable to encode pic state in 64bit in pic_levels."
> > > +#endif
> > > +    uint64_t pic_levels;
> > > +
> > >      qemu_irq *pic;
> > >  
> > >      /* This member isn't used. Just for save/load compatibility */
> > > @@ -254,25 +273,63 @@ PCIBus *i440fx_init(PCII440FXState **pi440fx_state, int *piix3_devfn, qemu_irq *
> > >  }
> > >  
> > >  /* PIIX3 PCI to ISA bridge */
> > > +static void piix3_set_irq_pic(PIIX3State *piix3, int pic_irq)
> > > +{
> > > +    qemu_set_irq(piix3->pic[pic_irq],
> > > +                 !!(piix3->pic_levels &
> > > +                    ((PIIX_NUM_PIRQS - 1) << (pic_irq * PIIX_NUM_PIRQS))));
> > > +}
> > > +
> > > +static void piix3_set_irq_level(PIIX3State *piix3, int irq_num, int level,
> > > +                                bool propagate)
> > 
> > This is called from piix3_set_irq_pic and gets INTX# (0 to PCI_NUM_PINS).
> 
> I used irq_num some places because of the existing code and pci.c.
> Here irq_num = PIRQ number. But irq_num = intx in pci_lost_get_pirq()
> Hmm should I avoid irq_num totally, and use intx, pirq, pic_irq?

Right, this might make it clearer.

> I hope the following clarifies the conversion.
> 
> A pci device asserts a interrupt pin of intx
>       |
>       V
> pci_set_irq()
>       |
>       V
> pci_slot_get_pirq() = bus->map_irq() gets (PCIDevice, intx)
>   returns pirq
>   This corresponds to how pci intx lines are connected to piix3 pirq pins
>       |
>       V
> piix3_set_irq() = bus->set_irq() gets pirq
>       |
>       V
> piix3_set_irq_levels() gets pirq
>   converts pirq# into pic irq
>   calls piix3_set_irq_pic() with pic_irq
>       |
>       V
> piix3_set_irq_pic() gets pic_irq
>       |
>       V
>    pic code
> 
> 
> thanks,

I think I get it.

> > > +{
> > > +    int pic_irq;
> > > +    uint64_t mask;
> > > +
> > > +    pic_irq = piix3->dev.config[PIIX_PIRQC + irq_num];
> > > +    if (pic_irq >= PIIX_NUM_PIC_IRQS) {
> > > +        return;
> > > +    }
> > > +
> > > +    mask = 1ULL << ((pic_irq * PIIX_NUM_PIRQS) + irq_num);
> > > +    piix3->pic_levels &= ~mask;
> > > +    piix3->pic_levels |= mask * !!level;
> > > +
> > > +    if (propagate) {
> > > +        piix3_set_irq_pic(piix3, pic_irq);
> > > +    }
> > > +}
> > >  
> > >  static void piix3_set_irq(void *opaque, int irq_num, int level)
> > >  {
> > > -    int i, pic_irq, pic_level;
> > >      PIIX3State *piix3 = opaque;
> > > +    piix3_set_irq_level(piix3, irq_num, level, true);
> > > +}
> > >  
> > > -    /* now we change the pic irq level according to the piix irq mappings */
> > > -    /* XXX: optimize */
> > > -    pic_irq = piix3->dev.config[0x60 + irq_num];
> > > -    if (pic_irq < 16) {
> > > -        /* The pic level is the logical OR of all the PCI irqs mapped
> > > -           to it */
> > > -        pic_level = 0;
> > > -        for (i = 0; i < 4; i++) {
> > > -            if (pic_irq == piix3->dev.config[0x60 + i]) {
> > > -                pic_level |= pci_bus_get_irq_level(piix3->dev.bus, i);
> > > -            }
> > > +/* irq routing is changed. so rebuild bitmap */
> > > +static void piix3_update_irq_levels(PIIX3State *piix3)
> > > +{
> > > +    int pirq;
> > > +
> > > +    piix3->pic_levels = 0;
> > > +    for (pirq = 0; pirq < PIIX_NUM_PIRQS; pirq++) {
> > > +        piix3_set_irq_level(piix3, pirq,
> > > +                            pci_bus_get_irq_level(piix3->dev.bus, pirq),
> > > +                            false);
> > 
> > Here it is called with PIRQ # 0 to PIIX_NUM_PIRQS.
> > 
> > > +    }
> > > +}
> > > +
> > > +static void piix3_write_config(PCIDevice *dev,
> > > +                               uint32_t address, uint32_t val, int len)
> > > +{
> > > +    pci_default_write_config(dev, address, val, len);
> > > +    if (ranges_overlap(address, len, PIIX_PIRQC, 4)) {
> > > +        PIIX3State *piix3 = DO_UPCAST(PIIX3State, dev, dev);
> > > +        int pic_irq;
> > > +        piix3_update_irq_levels(piix3);
> > > +        for (pic_irq = 0; pic_irq < PIIX_NUM_PIC_IRQS; pic_irq++) {
> > > +            piix3_set_irq_pic(piix3, pic_irq);
> > >          }
> > > -        qemu_set_irq(piix3->pic[pic_irq], pic_level);
> > >      }
> > >  }
> > >  
> > > @@ -312,6 +369,15 @@ static void piix3_reset(void *opaque)
> > >      pci_conf[0xab] = 0x00;
> > >      pci_conf[0xac] = 0x00;
> > >      pci_conf[0xae] = 0x00;
> > > +
> > > +    d->pic_levels = 0;
> > > +}
> > > +
> > > +static int piix3_post_load(void *opaque, int version_id)
> > > +{
> > > +    PIIX3State *piix3 = opaque;
> > > +    piix3_update_irq_levels(piix3);
> > > +    return 0;
> > >  }
> > >  
> > >  static void piix3_pre_save(void *opaque)
> > > @@ -330,6 +396,7 @@ static const VMStateDescription vmstate_piix3 = {
> > >      .version_id = 3,
> > >      .minimum_version_id = 2,
> > >      .minimum_version_id_old = 2,
> > > +    .post_load = piix3_post_load,
> > >      .pre_save = piix3_pre_save,
> > >      .fields      = (VMStateField []) {
> > >          VMSTATE_PCI_DEVICE(dev, PIIX3State),
> > > @@ -372,6 +439,7 @@ static PCIDeviceInfo i440fx_info[] = {
> > >          .qdev.no_user = 1,
> > >          .no_hotplug   = 1,
> > >          .init         = piix3_initfn,
> > > +        .config_write = piix3_write_config,
> > >      },{
> > >          /* end of list */
> > >      }
> > > 
> > 
> 
> -- 
> yamahata