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KVM: Intelligent device lookup on I/O bus 

Currently the method of dealing with an IO operation on a bus (PIO/MMIO)
is to call the read or write callback for each device registered
on the bus until we find a device which handles it.

Since the number of devices on a bus can be significant due to ioeventfds
and coalesced MMIO zones, this leads to a lot of overhead on each IO
operation.

Instead of registering devices, we now register ranges which points to
a device. Lookup is done using an efficient bsearch instead of a linear
search.

Performance test was conducted by comparing exit count per second with
200 ioeventfds created on one byte and the guest is trying to access a
different byte continuously (triggering usermode exits).
Before the patch the guest has achieved 259k exits per second, after the
patch the guest does 274k exits per second.

Cc: Avi Kivity <avi@redhat.com>
Cc: Marcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: Sasha Levin <levinsasha928@gmail.com>
Signed-off-by: Avi Kivity <avi@redhat.com>
This commit is contained in:
Sasha Levin 2011-07-27 16:00:48 +03:00 committed by Avi Kivity
parent 0d460ffc09
commit 743eeb0b01
9 changed files with 216 additions and 47 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

6
arch/x86/kvm/i8254.c
View File

@ -713,14 +713,16 @@ struct kvm_pit *kvm_create_pit(struct kvm *kvm, u32 flags)
kvm_register_irq_mask_notifier(kvm, 0, &pit->mask_notifier);
kvm_iodevice_init(&pit->dev, &pit_dev_ops);
ret = kvm_io_bus_register_dev(kvm, KVM_PIO_BUS, &pit->dev);
ret = kvm_io_bus_register_dev(kvm, KVM_PIO_BUS, KVM_PIT_BASE_ADDRESS,
KVM_PIT_MEM_LENGTH, &pit->dev);
if (ret < 0)
goto fail;
if (flags & KVM_PIT_SPEAKER_DUMMY) {
kvm_iodevice_init(&pit->speaker_dev, &speaker_dev_ops);
ret = kvm_io_bus_register_dev(kvm, KVM_PIO_BUS,
&pit->speaker_dev);
KVM_SPEAKER_BASE_ADDRESS, 4,
&pit->speaker_dev);
if (ret < 0)
goto fail_unregister;
}

108
arch/x86/kvm/i8259.c
View File

@ -459,15 +459,9 @@ static int picdev_in_range(gpa_t addr)
}
}
static inline struct kvm_pic *to_pic(struct kvm_io_device *dev)
{
return container_of(dev, struct kvm_pic, dev);
}
static int picdev_write(struct kvm_io_device *this,
static int picdev_write(struct kvm_pic *s,
gpa_t addr, int len, const void *val)
{
struct kvm_pic *s = to_pic(this);
unsigned char data = *(unsigned char *)val;
if (!picdev_in_range(addr))
return -EOPNOTSUPP;
@ -494,10 +488,9 @@ static int picdev_write(struct kvm_io_device *this,
return 0;
}
static int picdev_read(struct kvm_io_device *this,
static int picdev_read(struct kvm_pic *s,
gpa_t addr, int len, void *val)
{
struct kvm_pic *s = to_pic(this);
unsigned char data = 0;
if (!picdev_in_range(addr))
return -EOPNOTSUPP;
@ -525,6 +518,48 @@ static int picdev_read(struct kvm_io_device *this,
return 0;
}
static int picdev_master_write(struct kvm_io_device *dev,
gpa_t addr, int len, const void *val)
{
return picdev_write(container_of(dev, struct kvm_pic, dev_master),
addr, len, val);
}
static int picdev_master_read(struct kvm_io_device *dev,
gpa_t addr, int len, void *val)
{
return picdev_read(container_of(dev, struct kvm_pic, dev_master),
addr, len, val);
}
static int picdev_slave_write(struct kvm_io_device *dev,
gpa_t addr, int len, const void *val)
{
return picdev_write(container_of(dev, struct kvm_pic, dev_slave),
addr, len, val);
}
static int picdev_slave_read(struct kvm_io_device *dev,
gpa_t addr, int len, void *val)
{
return picdev_read(container_of(dev, struct kvm_pic, dev_slave),
addr, len, val);
}
static int picdev_eclr_write(struct kvm_io_device *dev,
gpa_t addr, int len, const void *val)
{
return picdev_write(container_of(dev, struct kvm_pic, dev_eclr),
addr, len, val);
}
static int picdev_eclr_read(struct kvm_io_device *dev,
gpa_t addr, int len, void *val)
{
return picdev_read(container_of(dev, struct kvm_pic, dev_eclr),
addr, len, val);
}
/*
* callback when PIC0 irq status changed
*/
@ -537,9 +572,19 @@ static void pic_irq_request(struct kvm *kvm, int level)
s->output = level;
}
static const struct kvm_io_device_ops picdev_ops = {
.read = picdev_read,
.write = picdev_write,
static const struct kvm_io_device_ops picdev_master_ops = {
.read = picdev_master_read,
.write = picdev_master_write,
};
static const struct kvm_io_device_ops picdev_slave_ops = {
.read = picdev_slave_read,
.write = picdev_slave_write,
};
static const struct kvm_io_device_ops picdev_eclr_ops = {
.read = picdev_eclr_read,
.write = picdev_eclr_write,
};
struct kvm_pic *kvm_create_pic(struct kvm *kvm)
@ -560,16 +605,39 @@ struct kvm_pic *kvm_create_pic(struct kvm *kvm)
/*
* Initialize PIO device
*/
kvm_iodevice_init(&s->dev, &picdev_ops);
kvm_iodevice_init(&s->dev_master, &picdev_master_ops);
kvm_iodevice_init(&s->dev_slave, &picdev_slave_ops);
kvm_iodevice_init(&s->dev_eclr, &picdev_eclr_ops);
mutex_lock(&kvm->slots_lock);
ret = kvm_io_bus_register_dev(kvm, KVM_PIO_BUS, &s->dev);
ret = kvm_io_bus_register_dev(kvm, KVM_PIO_BUS, 0x20, 2,
&s->dev_master);
if (ret < 0)
goto fail_unlock;
ret = kvm_io_bus_register_dev(kvm, KVM_PIO_BUS, 0xa0, 2, &s->dev_slave);
if (ret < 0)
goto fail_unreg_2;
ret = kvm_io_bus_register_dev(kvm, KVM_PIO_BUS, 0x4d0, 2, &s->dev_eclr);
if (ret < 0)
goto fail_unreg_1;
mutex_unlock(&kvm->slots_lock);
if (ret < 0) {
kfree(s);
return NULL;
}
return s;
fail_unreg_1:
kvm_io_bus_unregister_dev(kvm, KVM_PIO_BUS, &s->dev_slave);
fail_unreg_2:
kvm_io_bus_unregister_dev(kvm, KVM_PIO_BUS, &s->dev_master);
fail_unlock:
mutex_unlock(&kvm->slots_lock);
kfree(s);
return NULL;
}
void kvm_destroy_pic(struct kvm *kvm)
@ -577,7 +645,9 @@ void kvm_destroy_pic(struct kvm *kvm)
struct kvm_pic *vpic = kvm->arch.vpic;
if (vpic) {
kvm_io_bus_unregister_dev(kvm, KVM_PIO_BUS, &vpic->dev);
kvm_io_bus_unregister_dev(kvm, KVM_PIO_BUS, &vpic->dev_master);
kvm_io_bus_unregister_dev(kvm, KVM_PIO_BUS, &vpic->dev_slave);
kvm_io_bus_unregister_dev(kvm, KVM_PIO_BUS, &vpic->dev_eclr);
kvm->arch.vpic = NULL;
kfree(vpic);
}

4
arch/x86/kvm/irq.h
View File

@ -66,7 +66,9 @@ struct kvm_pic {
struct kvm *kvm;
struct kvm_kpic_state pics[2]; /* 0 is master pic, 1 is slave pic */
int output; /* intr from master PIC */
struct kvm_io_device dev;
struct kvm_io_device dev_master;
struct kvm_io_device dev_slave;
struct kvm_io_device dev_eclr;
void (*ack_notifier)(void *opaque, int irq);
unsigned long irq_states[16];
};

6
arch/x86/kvm/x86.c
View File

@ -3562,7 +3562,11 @@ long kvm_arch_vm_ioctl(struct file *filp,
if (r) {
mutex_lock(&kvm->slots_lock);
kvm_io_bus_unregister_dev(kvm, KVM_PIO_BUS,
&vpic->dev);
&vpic->dev_master);
kvm_io_bus_unregister_dev(kvm, KVM_PIO_BUS,
&vpic->dev_slave);
kvm_io_bus_unregister_dev(kvm, KVM_PIO_BUS,
&vpic->dev_eclr);
mutex_unlock(&kvm->slots_lock);
kfree(vpic);
goto create_irqchip_unlock;

18
include/linux/kvm_host.h
View File

@ -55,16 +55,16 @@ struct kvm;
struct kvm_vcpu;
extern struct kmem_cache *kvm_vcpu_cache;
/*
* It would be nice to use something smarter than a linear search, TBD...
* Thankfully we dont expect many devices to register (famous last words :),
* so until then it will suffice. At least its abstracted so we can change
* in one place.
*/
struct kvm_io_range {
gpa_t addr;
int len;
struct kvm_io_device *dev;
};
struct kvm_io_bus {
int dev_count;
#define NR_IOBUS_DEVS 300
struct kvm_io_device *devs[NR_IOBUS_DEVS];
struct kvm_io_range range[NR_IOBUS_DEVS];
};
enum kvm_bus {
@ -77,8 +77,8 @@ int kvm_io_bus_write(struct kvm *kvm, enum kvm_bus bus_idx, gpa_t addr,
int len, const void *val);
int kvm_io_bus_read(struct kvm *kvm, enum kvm_bus bus_idx, gpa_t addr, int len,
void *val);
int kvm_io_bus_register_dev(struct kvm *kvm, enum kvm_bus bus_idx,
struct kvm_io_device *dev);
int kvm_io_bus_register_dev(struct kvm *kvm, enum kvm_bus bus_idx, gpa_t addr,
int len, struct kvm_io_device *dev);
int kvm_io_bus_unregister_dev(struct kvm *kvm, enum kvm_bus bus_idx,
struct kvm_io_device *dev);

3
virt/kvm/coalesced_mmio.c
View File

@ -141,7 +141,8 @@ int kvm_vm_ioctl_register_coalesced_mmio(struct kvm *kvm,
dev->zone = *zone;
mutex_lock(&kvm->slots_lock);
ret = kvm_io_bus_register_dev(kvm, KVM_MMIO_BUS, &dev->dev);
ret = kvm_io_bus_register_dev(kvm, KVM_MMIO_BUS, zone->addr,
zone->size, &dev->dev);
if (ret < 0)
goto out_free_dev;
list_add_tail(&dev->list, &kvm->coalesced_zones);

3
virt/kvm/eventfd.c
View File

@ -586,7 +586,8 @@ kvm_assign_ioeventfd(struct kvm *kvm, struct kvm_ioeventfd *args)
kvm_iodevice_init(&p->dev, &ioeventfd_ops);
ret = kvm_io_bus_register_dev(kvm, bus_idx, &p->dev);
ret = kvm_io_bus_register_dev(kvm, bus_idx, p->addr, p->length,
&p->dev);
if (ret < 0)
goto unlock_fail;

3
virt/kvm/ioapic.c
View File

@ -394,7 +394,8 @@ int kvm_ioapic_init(struct kvm *kvm)
kvm_iodevice_init(&ioapic->dev, &ioapic_mmio_ops);
ioapic->kvm = kvm;
mutex_lock(&kvm->slots_lock);
ret = kvm_io_bus_register_dev(kvm, KVM_MMIO_BUS, &ioapic->dev);
ret = kvm_io_bus_register_dev(kvm, KVM_MMIO_BUS, ioapic->base_address,
IOAPIC_MEM_LENGTH, &ioapic->dev);
mutex_unlock(&kvm->slots_lock);
if (ret < 0) {
kvm->arch.vioapic = NULL;

112
virt/kvm/kvm_main.c
View File

@ -47,6 +47,8 @@
#include <linux/srcu.h>
#include <linux/hugetlb.h>
#include <linux/slab.h>
#include <linux/sort.h>
#include <linux/bsearch.h>
#include <asm/processor.h>
#include <asm/io.h>
@ -2391,24 +2393,92 @@ static void kvm_io_bus_destroy(struct kvm_io_bus *bus)
int i;
for (i = 0; i < bus->dev_count; i++) {
struct kvm_io_device *pos = bus->devs[i];
struct kvm_io_device *pos = bus->range[i].dev;
kvm_iodevice_destructor(pos);
}
kfree(bus);
}
int kvm_io_bus_sort_cmp(const void *p1, const void *p2)
{
const struct kvm_io_range *r1 = p1;
const struct kvm_io_range *r2 = p2;
if (r1->addr < r2->addr)
return -1;
if (r1->addr + r1->len > r2->addr + r2->len)
return 1;
return 0;
}
int kvm_io_bus_insert_dev(struct kvm_io_bus *bus, struct kvm_io_device *dev,
gpa_t addr, int len)
{
if (bus->dev_count == NR_IOBUS_DEVS)
return -ENOSPC;
bus->range[bus->dev_count++] = (struct kvm_io_range) {
.addr = addr,
.len = len,
.dev = dev,
};
sort(bus->range, bus->dev_count, sizeof(struct kvm_io_range),
kvm_io_bus_sort_cmp, NULL);
return 0;
}
int kvm_io_bus_get_first_dev(struct kvm_io_bus *bus,
gpa_t addr, int len)
{
struct kvm_io_range *range, key;
int off;
key = (struct kvm_io_range) {
.addr = addr,
.len = len,
};
range = bsearch(&key, bus->range, bus->dev_count,
sizeof(struct kvm_io_range), kvm_io_bus_sort_cmp);
if (range == NULL)
return -ENOENT;
off = range - bus->range;
while (off > 0 && kvm_io_bus_sort_cmp(&key, &bus->range[off-1]) == 0)
off--;
return off;
}
/* kvm_io_bus_write - called under kvm->slots_lock */
int kvm_io_bus_write(struct kvm *kvm, enum kvm_bus bus_idx, gpa_t addr,
int len, const void *val)
{
int i;
int idx;
struct kvm_io_bus *bus;
struct kvm_io_range range;
range = (struct kvm_io_range) {
.addr = addr,
.len = len,
};
bus = srcu_dereference(kvm->buses[bus_idx], &kvm->srcu);
for (i = 0; i < bus->dev_count; i++)
if (!kvm_iodevice_write(bus->devs[i], addr, len, val))
idx = kvm_io_bus_get_first_dev(bus, addr, len);
if (idx < 0)
return -EOPNOTSUPP;
while (idx < bus->dev_count &&
kvm_io_bus_sort_cmp(&range, &bus->range[idx]) == 0) {
if (!kvm_iodevice_write(bus->range[idx].dev, addr, len, val))
return 0;
idx++;
}
return -EOPNOTSUPP;
}
@ -2416,19 +2486,33 @@ int kvm_io_bus_write(struct kvm *kvm, enum kvm_bus bus_idx, gpa_t addr,
int kvm_io_bus_read(struct kvm *kvm, enum kvm_bus bus_idx, gpa_t addr,
int len, void *val)
{
int i;
int idx;
struct kvm_io_bus *bus;
struct kvm_io_range range;
range = (struct kvm_io_range) {
.addr = addr,
.len = len,
};
bus = srcu_dereference(kvm->buses[bus_idx], &kvm->srcu);
for (i = 0; i < bus->dev_count; i++)
if (!kvm_iodevice_read(bus->devs[i], addr, len, val))
idx = kvm_io_bus_get_first_dev(bus, addr, len);
if (idx < 0)
return -EOPNOTSUPP;
while (idx < bus->dev_count &&
kvm_io_bus_sort_cmp(&range, &bus->range[idx]) == 0) {
if (!kvm_iodevice_read(bus->range[idx].dev, addr, len, val))
return 0;
idx++;
}
return -EOPNOTSUPP;
}
/* Caller must hold slots_lock. */
int kvm_io_bus_register_dev(struct kvm *kvm, enum kvm_bus bus_idx,
struct kvm_io_device *dev)
int kvm_io_bus_register_dev(struct kvm *kvm, enum kvm_bus bus_idx, gpa_t addr,
int len, struct kvm_io_device *dev)
{
struct kvm_io_bus *new_bus, *bus;
@ -2440,7 +2524,7 @@ int kvm_io_bus_register_dev(struct kvm *kvm, enum kvm_bus bus_idx,
if (!new_bus)
return -ENOMEM;
memcpy(new_bus, bus, sizeof(struct kvm_io_bus));
new_bus->devs[new_bus->dev_count++] = dev;
kvm_io_bus_insert_dev(new_bus, dev, addr, len);
rcu_assign_pointer(kvm->buses[bus_idx], new_bus);
synchronize_srcu_expedited(&kvm->srcu);
kfree(bus);
@ -2464,9 +2548,13 @@ int kvm_io_bus_unregister_dev(struct kvm *kvm, enum kvm_bus bus_idx,
r = -ENOENT;
for (i = 0; i < new_bus->dev_count; i++)
if (new_bus->devs[i] == dev) {
if (new_bus->range[i].dev == dev) {
r = 0;
new_bus->devs[i] = new_bus->devs[--new_bus->dev_count];
new_bus->dev_count--;
new_bus->range[i] = new_bus->range[new_bus->dev_count];
sort(new_bus->range, new_bus->dev_count,
sizeof(struct kvm_io_range),
kvm_io_bus_sort_cmp, NULL);
break;
}