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.
Changes in V3:
- Small fix in error path of i8259.
Changes in V2:
- Only register a device once.
- Support for multiple devices using same range.
- Added performance benchmark.
- Using bsearch() and sort() found in /lib/.
Cc: Avi Kivity <a...@redhat.com>
Cc: Marcelo Tosatti <mtosa...@redhat.com>
Signed-off-by: Sasha Levin <levinsasha...@gmail.com>
---
arch/x86/kvm/i8254.c | 5 +-
arch/x86/kvm/i8259.c | 56 ++++++++++++++++++----
arch/x86/kvm/irq.h | 4 +-
arch/x86/kvm/x86.c | 6 ++-
include/linux/kvm_host.h | 18 ++++----
virt/kvm/coalesced_mmio.c | 3 +-
virt/kvm/eventfd.c | 3 +-
virt/kvm/ioapic.c | 3 +-
virt/kvm/kvm_main.c | 112 ++++++++++++++++++++++++++++++++++++++++-----
9 files changed, 171 insertions(+), 39 deletions(-)
diff --git a/arch/x86/kvm/i8254.c b/arch/x86/kvm/i8254.c
index efad723..094e057 100644
--- a/arch/x86/kvm/i8254.c
+++ b/arch/x86/kvm/i8254.c
@@ -713,14 +713,15 @@ 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;
}
diff --git a/arch/x86/kvm/i8259.c b/arch/x86/kvm/i8259.c
index 19fe855..9e18698 100644
--- a/arch/x86/kvm/i8259.c
+++ b/arch/x86/kvm/i8259.c
@@ -459,15 +459,27 @@ static int picdev_in_range(gpa_t addr)
}
}
-static inline struct kvm_pic *to_pic(struct kvm_io_device *dev)
+static inline struct kvm_pic *to_pic(struct kvm_io_device *dev, gpa_t addr)
{
- return container_of(dev, struct kvm_pic, dev);
+ switch (addr) {
+ case 0x20:
+ case 0x21:
+ return container_of(dev, struct kvm_pic, dev_master);
+ case 0xa0:
+ case 0xa1:
+ return container_of(dev, struct kvm_pic, dev_slave);
+ case 0x4d0:
+ case 0x4d1:
+ return container_of(dev, struct kvm_pic, dev_eclr);
+ }
+
+ return NULL;
}
static int picdev_write(struct kvm_io_device *this,
gpa_t addr, int len, const void *val)
{
- struct kvm_pic *s = to_pic(this);
+ struct kvm_pic *s = to_pic(this, addr);
unsigned char data = *(unsigned char *)val;
if (!picdev_in_range(addr))
return -EOPNOTSUPP;
@@ -497,7 +509,7 @@ static int picdev_write(struct kvm_io_device *this,
static int picdev_read(struct kvm_io_device *this,
gpa_t addr, int len, void *val)
{
- struct kvm_pic *s = to_pic(this);
+ struct kvm_pic *s = to_pic(this, addr);
unsigned char data = 0;
if (!picdev_in_range(addr))
return -EOPNOTSUPP;
@@ -560,16 +572,36 @@ 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_ops);
+ kvm_iodevice_init(&s->dev_slave, &picdev_ops);
+ kvm_iodevice_init(&s->dev_eclr, &picdev_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_unlock;
+
+ ret = kvm_io_bus_register_dev(kvm, KVM_PIO_BUS, 0x4d0, 2, &s->dev_eclr);
+ if (ret < 0)
+ goto fail_unlock;
+
mutex_unlock(&kvm->slots_lock);
- if (ret < 0) {
- kfree(s);
- return NULL;
- }
return s;
+
+fail_unlock:
+
+ mutex_unlock(&kvm->slots_lock);
+ kvm_io_bus_unregister_dev(kvm, KVM_PIO_BUS, &s->dev_master);
+ kvm_io_bus_unregister_dev(kvm, KVM_PIO_BUS, &s->dev_slave);
+ kvm_io_bus_unregister_dev(kvm, KVM_PIO_BUS, &s->dev_eclr);
+
+ kfree(s);
+
+ return NULL;
}
void kvm_destroy_pic(struct kvm *kvm)
@@ -577,7 +609,9 @@ 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);
}
diff --git a/arch/x86/kvm/irq.h b/arch/x86/kvm/irq.h
index 53e2d08..2086f2b 100644
--- a/arch/x86/kvm/irq.h
+++ b/arch/x86/kvm/irq.h
@@ -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];
};
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index e80f0d7..4cea9cf 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -3561,7 +3561,11 @@ 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;
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index ff4d406..d0e42f3 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -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);
diff --git a/virt/kvm/coalesced_mmio.c b/virt/kvm/coalesced_mmio.c
index 2316ec1..a6ec206 100644
--- a/virt/kvm/coalesced_mmio.c
+++ b/virt/kvm/coalesced_mmio.c
@@ -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);
diff --git a/virt/kvm/eventfd.c b/virt/kvm/eventfd.c
index 73358d2..f59c1e8 100644
--- a/virt/kvm/eventfd.c
+++ b/virt/kvm/eventfd.c
@@ -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;
diff --git a/virt/kvm/ioapic.c b/virt/kvm/ioapic.c
index 8df1ca1..86aeea1 100644
--- a/virt/kvm/ioapic.c
+++ b/virt/kvm/ioapic.c
@@ -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;
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index aefdda3..0c228f4 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -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 +2393,94 @@ 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)
+{
+ int i;
+
+ 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 +2488,33 @@ 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 +2526,7 @@ 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 +2550,11 @@ 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->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;
}
--
1.7.6
--
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