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qemu-e2k/hw/virtio.h
Stefan Hajnoczi 25db9ebe15 virtio-pci: Use ioeventfd for virtqueue notify 
Virtqueue notify is currently handled synchronously in userspace virtio.  This
prevents the vcpu from executing guest code while hardware emulation code
handles the notify.

On systems that support KVM, the ioeventfd mechanism can be used to make
virtqueue notify a lightweight exit by deferring hardware emulation to the
iothread and allowing the VM to continue execution.  This model is similar to
how vhost receives virtqueue notifies.

The result of this change is improved performance for userspace virtio devices.
Virtio-blk throughput increases especially for multithreaded scenarios and
virtio-net transmit throughput increases substantially.

Some virtio devices are known to have guest drivers which expect a notify to be
processed synchronously and spin waiting for completion.
For virtio-net, this also seems to interact with the guest stack in strange
ways so that TCP throughput for small message sizes (~200bytes)
is harmed. Only enable ioeventfd for virtio-blk for now.

Care must be taken not to interfere with vhost-net, which uses host
notifiers.  If the set_host_notifier() API is used by a device
virtio-pci will disable virtio-ioeventfd and let the device deal with
host notifiers as it wishes.

Finally, there used to be a limit of 6 KVM io bus devices inside the
kernel.  On such a kernel, don't use ioeventfd for virtqueue host
notification since the limit is reached too easily.  This ensures that
existing vhost-net setups (which always use ioeventfd) have ioeventfds
available so they can continue to work.

After migration and on VM change state (running/paused) virtio-ioeventfd
will enable/disable itself.

 * VIRTIO_CONFIG_S_DRIVER_OK -> enable virtio-ioeventfd
 * !VIRTIO_CONFIG_S_DRIVER_OK -> disable virtio-ioeventfd
 * virtio_pci_set_host_notifier() -> disable virtio-ioeventfd
 * vm_change_state(running=0) -> disable virtio-ioeventfd
 * vm_change_state(running=1) -> enable virtio-ioeventfd

Signed-off-by: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
2011-01-10 14:44:16 +02:00

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/*
* Virtio Support
*
* Copyright IBM, Corp. 2007
*
* Authors:
* Anthony Liguori <aliguori@us.ibm.com>
*
* This work is licensed under the terms of the GNU GPL, version 2. See
* the COPYING file in the top-level directory.
*
*/
#ifndef _QEMU_VIRTIO_H
#define _QEMU_VIRTIO_H
#include "hw.h"
#include "net.h"
#include "qdev.h"
#include "sysemu.h"
#include "block_int.h"
#include "event_notifier.h"
#ifdef CONFIG_LINUX
#include "9p.h"
#endif
/* from Linux's linux/virtio_config.h */
/* Status byte for guest to report progress, and synchronize features. */
/* We have seen device and processed generic fields (VIRTIO_CONFIG_F_VIRTIO) */
#define VIRTIO_CONFIG_S_ACKNOWLEDGE 1
/* We have found a driver for the device. */
#define VIRTIO_CONFIG_S_DRIVER 2
/* Driver has used its parts of the config, and is happy */
#define VIRTIO_CONFIG_S_DRIVER_OK 4
/* We've given up on this device. */
#define VIRTIO_CONFIG_S_FAILED 0x80
/* Some virtio feature bits (currently bits 28 through 31) are reserved for the
* transport being used (eg. virtio_ring), the rest are per-device feature bits. */
#define VIRTIO_TRANSPORT_F_START 28
#define VIRTIO_TRANSPORT_F_END 32
/* We notify when the ring is completely used, even if the guest is suppressing
* callbacks */
#define VIRTIO_F_NOTIFY_ON_EMPTY 24
/* We support indirect buffer descriptors */
#define VIRTIO_RING_F_INDIRECT_DESC 28
/* A guest should never accept this. It implies negotiation is broken. */
#define VIRTIO_F_BAD_FEATURE 30
/* from Linux's linux/virtio_ring.h */
/* This marks a buffer as continuing via the next field. */
#define VRING_DESC_F_NEXT 1
/* This marks a buffer as write-only (otherwise read-only). */
#define VRING_DESC_F_WRITE 2
/* This means the buffer contains a list of buffer descriptors. */
#define VRING_DESC_F_INDIRECT 4
/* This means don't notify other side when buffer added. */
#define VRING_USED_F_NO_NOTIFY 1
/* This means don't interrupt guest when buffer consumed. */
#define VRING_AVAIL_F_NO_INTERRUPT 1
struct VirtQueue;
static inline target_phys_addr_t vring_align(target_phys_addr_t addr,
unsigned long align)
{
return (addr + align - 1) & ~(align - 1);
}
typedef struct VirtQueue VirtQueue;
#define VIRTQUEUE_MAX_SIZE 1024
typedef struct VirtQueueElement
{
unsigned int index;
unsigned int out_num;
unsigned int in_num;
target_phys_addr_t in_addr[VIRTQUEUE_MAX_SIZE];
target_phys_addr_t out_addr[VIRTQUEUE_MAX_SIZE];
struct iovec in_sg[VIRTQUEUE_MAX_SIZE];
struct iovec out_sg[VIRTQUEUE_MAX_SIZE];
} VirtQueueElement;
typedef struct {
void (*notify)(void * opaque, uint16_t vector);
void (*save_config)(void * opaque, QEMUFile *f);
void (*save_queue)(void * opaque, int n, QEMUFile *f);
int (*load_config)(void * opaque, QEMUFile *f);
int (*load_queue)(void * opaque, int n, QEMUFile *f);
unsigned (*get_features)(void * opaque);
int (*set_guest_notifiers)(void * opaque, bool assigned);
int (*set_host_notifier)(void * opaque, int n, bool assigned);
void (*vmstate_change)(void * opaque, bool running);
} VirtIOBindings;
#define VIRTIO_PCI_QUEUE_MAX 64
#define VIRTIO_NO_VECTOR 0xffff
struct VirtIODevice
{
const char *name;
uint8_t status;
uint8_t isr;
uint16_t queue_sel;
uint32_t guest_features;
size_t config_len;
void *config;
uint16_t config_vector;
int nvectors;
uint32_t (*get_features)(VirtIODevice *vdev, uint32_t requested_features);
uint32_t (*bad_features)(VirtIODevice *vdev);
void (*set_features)(VirtIODevice *vdev, uint32_t val);
void (*get_config)(VirtIODevice *vdev, uint8_t *config);
void (*set_config)(VirtIODevice *vdev, const uint8_t *config);
void (*reset)(VirtIODevice *vdev);
void (*set_status)(VirtIODevice *vdev, uint8_t val);
VirtQueue *vq;
const VirtIOBindings *binding;
void *binding_opaque;
uint16_t device_id;
bool vm_running;
VMChangeStateEntry *vmstate;
};
static inline void virtio_set_status(VirtIODevice *vdev, uint8_t val)
{
if (vdev->set_status) {
vdev->set_status(vdev, val);
}
vdev->status = val;
}
VirtQueue *virtio_add_queue(VirtIODevice *vdev, int queue_size,
void (*handle_output)(VirtIODevice *,
VirtQueue *));
void virtqueue_push(VirtQueue *vq, const VirtQueueElement *elem,
unsigned int len);
void virtqueue_flush(VirtQueue *vq, unsigned int count);
void virtqueue_fill(VirtQueue *vq, const VirtQueueElement *elem,
unsigned int len, unsigned int idx);
void virtqueue_map_sg(struct iovec *sg, target_phys_addr_t *addr,
size_t num_sg, int is_write);
int virtqueue_pop(VirtQueue *vq, VirtQueueElement *elem);
int virtqueue_avail_bytes(VirtQueue *vq, int in_bytes, int out_bytes);
void virtio_notify(VirtIODevice *vdev, VirtQueue *vq);
void virtio_save(VirtIODevice *vdev, QEMUFile *f);
int virtio_load(VirtIODevice *vdev, QEMUFile *f);
void virtio_cleanup(VirtIODevice *vdev);
void virtio_notify_config(VirtIODevice *vdev);
void virtio_queue_set_notification(VirtQueue *vq, int enable);
int virtio_queue_ready(VirtQueue *vq);
int virtio_queue_empty(VirtQueue *vq);
/* Host binding interface. */
VirtIODevice *virtio_common_init(const char *name, uint16_t device_id,
size_t config_size, size_t struct_size);
uint32_t virtio_config_readb(VirtIODevice *vdev, uint32_t addr);
uint32_t virtio_config_readw(VirtIODevice *vdev, uint32_t addr);
uint32_t virtio_config_readl(VirtIODevice *vdev, uint32_t addr);
void virtio_config_writeb(VirtIODevice *vdev, uint32_t addr, uint32_t data);
void virtio_config_writew(VirtIODevice *vdev, uint32_t addr, uint32_t data);
void virtio_config_writel(VirtIODevice *vdev, uint32_t addr, uint32_t data);
void virtio_queue_set_addr(VirtIODevice *vdev, int n, target_phys_addr_t addr);
target_phys_addr_t virtio_queue_get_addr(VirtIODevice *vdev, int n);
int virtio_queue_get_num(VirtIODevice *vdev, int n);
void virtio_queue_notify(VirtIODevice *vdev, int n);
uint16_t virtio_queue_vector(VirtIODevice *vdev, int n);
void virtio_queue_set_vector(VirtIODevice *vdev, int n, uint16_t vector);
void virtio_reset(void *opaque);
void virtio_update_irq(VirtIODevice *vdev);
void virtio_bind_device(VirtIODevice *vdev, const VirtIOBindings *binding,
void *opaque);
/* Base devices. */
VirtIODevice *virtio_blk_init(DeviceState *dev, BlockConf *conf);
struct virtio_net_conf;
VirtIODevice *virtio_net_init(DeviceState *dev, NICConf *conf,
struct virtio_net_conf *net);
VirtIODevice *virtio_serial_init(DeviceState *dev, uint32_t max_nr_ports);
VirtIODevice *virtio_balloon_init(DeviceState *dev);
#ifdef CONFIG_LINUX
VirtIODevice *virtio_9p_init(DeviceState *dev, V9fsConf *conf);
#endif
void virtio_net_exit(VirtIODevice *vdev);
void virtio_blk_exit(VirtIODevice *vdev);
void virtio_serial_exit(VirtIODevice *vdev);
#define DEFINE_VIRTIO_COMMON_FEATURES(_state, _field) \
DEFINE_PROP_BIT("indirect_desc", _state, _field, \
VIRTIO_RING_F_INDIRECT_DESC, true)
target_phys_addr_t virtio_queue_get_desc_addr(VirtIODevice *vdev, int n);
target_phys_addr_t virtio_queue_get_avail_addr(VirtIODevice *vdev, int n);
target_phys_addr_t virtio_queue_get_used_addr(VirtIODevice *vdev, int n);
target_phys_addr_t virtio_queue_get_ring_addr(VirtIODevice *vdev, int n);
target_phys_addr_t virtio_queue_get_desc_size(VirtIODevice *vdev, int n);
target_phys_addr_t virtio_queue_get_avail_size(VirtIODevice *vdev, int n);
target_phys_addr_t virtio_queue_get_used_size(VirtIODevice *vdev, int n);
target_phys_addr_t virtio_queue_get_ring_size(VirtIODevice *vdev, int n);
uint16_t virtio_queue_get_last_avail_idx(VirtIODevice *vdev, int n);
void virtio_queue_set_last_avail_idx(VirtIODevice *vdev, int n, uint16_t idx);
VirtQueue *virtio_get_queue(VirtIODevice *vdev, int n);
EventNotifier *virtio_queue_get_guest_notifier(VirtQueue *vq);
EventNotifier *virtio_queue_get_host_notifier(VirtQueue *vq);
void virtio_queue_notify_vq(VirtQueue *vq);
void virtio_irq(VirtQueue *vq);
#endif
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