Xen PV Guest interrupt

紧接这一篇：

http://blog.youkuaiyun.com/snailhit/archive/2010/12/28/6101827.aspx

当在PV Guest里运行cat /proc/interrupts查看中断设置情况是，会发现中断号不是从0开始的，而是从256开始的。典型的如下：

CPU0
256: 111925 Dynamic-irq timer0 （VM只有一个VCPU，若是SMP-VM，则有timer1, timer2, ...）
257: 0 Dynamic-irq resched0
258: 0 Dynamic-irq callfunc0

-----

... timer1, resched1, callfunc1, ...

-----
259: 270 Dynamic-irq xenbus
260: 1801 Dynamic-irq xencons
261: 3616 Dynamic-irq blkif
262: 7756 Dynamic-irq eth0
NMI:0
LOC:0
ERR:0
MIS:0

都是dynamic-irq，那么physical irq跑哪儿去了...? 原来，在PV guest中，所有的phyisical IRQ都被cut掉了，所有的都有dynamic IRQ来负责：

#define NR_DYNIRQS256

#define NR_IRQS(NR_PIRQS + NR_DYNIRQS)

在domain 0下运行 cat /proc/interrupts:

CPU0 CPU1 CPU2 CPU3
1: 3196 0 0 0 Phys-level i8042 （键盘..?）
6: 3 0 0 0 Phys-level floppy
8: 0 0 0 0 Phys-level rtc0 （rtc时钟）
12: 4 0 0 0 Phys-level i8042（鼠标..?）
14: 21648 26431 0 0 Phys-level ata_piix （硬盘）
15: 317748 19659 0 0 Phys-level ata_piix
16: 407 0 0 0 Phys-level ehci_hcd:usb2, uhci_hcd:usb3, uhci_hcd:usb6, HDA Intel
17: 0 0 0 0 Phys-level uhci_hcd:usb4, uhci_hcd:usb7
18: 73797 0 0 0 Phys-level ehci_hcd:usb1, uhci_hcd:usb5, uhci_hcd:usb8, ata_piix
------------

439: 23348 0 0 0 Phys-level peth0
440: 30292618 929005 656343 640930 Dynamic-percpu timer
441: 338983 738843 598292 605525 Dynamic-percpu resched
442: 23 196 233 221 Dynamic-percpu callfunc
443: 23559 2526 1132 865 Dynamic-percpu call1func
444: 0 0 0 0 Dynamic-percpu reboot
445: 1144 476 212 145 Dynamic-percpu spinlock
446: 0 0 0 0 Dynamic-level mce
447: 283 0 0 0 Dynamic-level console
448: 78 463 61 0 Dynamic-level xenbus

--
449: 804 987 0 0 Dynamic-level blkif-backend
450: 5731 1906 0 0 Dynamic-level vif1.0
--

451 .... blkif-backend

450 .... vif2.0

--

NMI: 0 0 0 0 Non-maskable interrupts
RES: 338983 738844 598293 605526 Rescheduling interrupts
CAL: 23582 2722 1365 1086 Function call interrupts
MCE: 0 0 0 0 Machine check exceptions
MCP: 1 1 1 1 Machine check polls

看Guest启动后，如何初始化irq_descriptor[NR_IRQS] (linux/driver/xen/core/evtchn.c, xen_init_IRQ):

/* Dynamic IRQ space is currently unbound. Zero the refcnts. */
for (i = DYNIRQ_BASE; i < (DYNIRQ_BASE + NR_DYNIRQS); i++) {
irq_bindcount[i] = 0;

irq_desc[i].status = IRQ_DISABLED|IRQ_NOPROBE;
irq_desc[i].action = NULL;
irq_desc[i].depth = 1;
irq_desc[i].chip = &dynirq_type;
}

static struct hw_interrupt_type dynirq_type = {
.typename = "Dynamic-irq",
.startup = startup_dynirq,
.shutdown = shutdown_dynirq,
.enable = enable_dynirq,
.disable = disable_dynirq,
.ack = ack_dynirq,
.end = end_dynirq,
.set_affinity = set_affinity_irq,
.retrigger = resend_irq_on_evtchn,
};

-----------------------

对于physical IRQ:

/* Phys IRQ space is statically bound (1:1 mapping). Nail refcnts. */
for (i = PIRQ_BASE; i < (PIRQ_BASE + NR_PIRQS); i++) {
irq_bindcount[i] = 1;

if (!identity_mapped_irq(i))
continue;

#ifdef RTC_IRQ
/* If not domain 0, force our RTC driver to fail its probe. */
if (i - PIRQ_BASE == RTC_IRQ && !is_initial_xendomain())
continue;
#endif

irq_desc[i].status = IRQ_DISABLED;
irq_desc[i].action = NULL;
irq_desc[i].depth = 1;
irq_desc[i].chip = &pirq_type;
}

static struct hw_interrupt_type pirq_type = {
.typename = "Phys-irq",
.startup = startup_pirq,
.shutdown = shutdown_pirq,
.enable = enable_pirq,
.disable = disable_pirq,
.ack = ack_pirq,
.end = end_pirq,
.set_affinity = set_affinity_irq,
.retrigger = resend_irq_on_evtchn,
};

对于不是driver domain的guest VM，rtc(real-time-clock)直接被禁掉了，时钟由VIRQ_TIMER来接管 (见linux/arch/arch/i386/kernel/time-xen.c, local_setup_timer)

physical irq 通过evtchn_register_pirq来注册

--------------------------------------

为什么是dynamic的：每一次分配，都要先去找unbound irq

static int find_unbound_irq(void)
{
static int warned;
int irq;

for (irq = DYNIRQ_BASE; irq < (DYNIRQ_BASE + NR_DYNIRQS); irq++)
if (irq_bindcount[irq] == 0)
return irq;

return -ENOSPC;
}

找到之后，通过hypercall想去和VM的evtchn来bind （有Xen来做的事情），结果Xen也要dynamic的找get_free_port

for ( port = 0; port_is_valid(d, port); port++ )
if ( evtchn_from_port(d, port)->state == ECS_FREE )
return port;