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vhost: logs sharing 

Currently we allocate one vhost log per vhost device. This is sub
optimal when:

- Guest has several device with vhost as backend
- Guest has multiqueue devices

In the above cases, we can avoid the memory allocation by sharing a
single vhost log among all the vhost devices. This is done through:

- Introducing a new vhost_log structure with refcnt inside.
- Using a global pointer to vhost_log structure that will be used. And
  introduce helper to get the log with expected log size and helper to
- drop the refcnt to the old log.
- Each vhost device still keep track of a pointer to the log that was
  used.

With above, if no resize happens, all vhost device will share a single
vhost log. During resize, a new vhost_log structure will be allocated
and made for the global pointer. And each vhost devices will drop the
refcnt to the old log.

Tested by doing scp during migration for a 2 queues virtio-net-pci.

Cc: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Jason Wang <jasowang@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
This commit is contained in:
Jason Wang 2015-06-04 05:28:46 -04:00 committed by Michael S. Tsirkin
parent 6e7d82497d
commit 309750fad5
2 changed files with 66 additions and 19 deletions
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77
hw/virtio/vhost.c
View File

@ -22,15 +22,19 @@
#include "hw/virtio/virtio-bus.h"
#include "migration/migration.h"
static struct vhost_log *vhost_log;
static void vhost_dev_sync_region(struct vhost_dev *dev,
MemoryRegionSection *section,
uint64_t mfirst, uint64_t mlast,
uint64_t rfirst, uint64_t rlast)
{
vhost_log_chunk_t *log = dev->log->log;
uint64_t start = MAX(mfirst, rfirst);
uint64_t end = MIN(mlast, rlast);
vhost_log_chunk_t *from = dev->log + start / VHOST_LOG_CHUNK;
vhost_log_chunk_t *to = dev->log + end / VHOST_LOG_CHUNK + 1;
vhost_log_chunk_t *from = log + start / VHOST_LOG_CHUNK;
vhost_log_chunk_t *to = log + end / VHOST_LOG_CHUNK + 1;
uint64_t addr = (start / VHOST_LOG_CHUNK) * VHOST_LOG_CHUNK;
if (end < start) {
@ -280,22 +284,57 @@ static uint64_t vhost_get_log_size(struct vhost_dev *dev)
}
return log_size;
}
static struct vhost_log *vhost_log_alloc(uint64_t size)
{
struct vhost_log *log = g_malloc0(sizeof *log + size * sizeof(*(log->log)));
log->size = size;
log->refcnt = 1;
return log;
}
static struct vhost_log *vhost_log_get(uint64_t size)
{
if (!vhost_log || vhost_log->size != size) {
vhost_log = vhost_log_alloc(size);
} else {
++vhost_log->refcnt;
}
return vhost_log;
}
static void vhost_log_put(struct vhost_dev *dev, bool sync)
{
struct vhost_log *log = dev->log;
if (!log) {
return;
}
--log->refcnt;
if (log->refcnt == 0) {
/* Sync only the range covered by the old log */
if (dev->log_size && sync) {
vhost_log_sync_range(dev, 0, dev->log_size * VHOST_LOG_CHUNK - 1);
}
if (vhost_log == log) {
vhost_log = NULL;
}
g_free(log);
}
}
static inline void vhost_dev_log_resize(struct vhost_dev* dev, uint64_t size)
{
vhost_log_chunk_t *log;
uint64_t log_base;
struct vhost_log *log = vhost_log_get(size);
uint64_t log_base = (uintptr_t)log->log;
int r;
log = g_malloc0(size * sizeof *log);
log_base = (uintptr_t)log;
r = dev->vhost_ops->vhost_call(dev, VHOST_SET_LOG_BASE, &log_base);
assert(r >= 0);
/* Sync only the range covered by the old log */
if (dev->log_size) {
vhost_log_sync_range(dev, 0, dev->log_size * VHOST_LOG_CHUNK - 1);
}
g_free(dev->log);
vhost_log_put(dev, true);
dev->log = log;
dev->log_size = size;
}
@ -601,7 +640,7 @@ static int vhost_migration_log(MemoryListener *listener, int enable)
if (r < 0) {
return r;
}
g_free(dev->log);
vhost_log_put(dev, false);
dev->log = NULL;
dev->log_size = 0;
} else {
@ -1060,10 +1099,10 @@ int vhost_dev_start(struct vhost_dev *hdev, VirtIODevice *vdev)
uint64_t log_base;
hdev->log_size = vhost_get_log_size(hdev);
hdev->log = hdev->log_size ?
g_malloc0(hdev->log_size * sizeof *hdev->log) : NULL;
log_base = (uintptr_t)hdev->log;
r = hdev->vhost_ops->vhost_call(hdev, VHOST_SET_LOG_BASE, &log_base);
hdev->log = vhost_log_get(hdev->log_size);
log_base = (uintptr_t)hdev->log->log;
r = hdev->vhost_ops->vhost_call(hdev, VHOST_SET_LOG_BASE,
hdev->log_size ? &log_base : NULL);
if (r < 0) {
r = -errno;
goto fail_log;
@ -1072,6 +1111,9 @@ int vhost_dev_start(struct vhost_dev *hdev, VirtIODevice *vdev)
return 0;
fail_log:
if (hdev->log_size) {
vhost_log_put(hdev, false);
}
fail_vq:
while (--i >= 0) {
vhost_virtqueue_stop(hdev,
@ -1098,10 +1140,9 @@ void vhost_dev_stop(struct vhost_dev *hdev, VirtIODevice *vdev)
hdev->vqs + i,
hdev->vq_index + i);
}
vhost_log_sync_range(hdev, 0, ~0x0ull);
vhost_log_put(hdev, true);
hdev->started = false;
g_free(hdev->log);
hdev->log = NULL;
hdev->log_size = 0;
}

8
include/hw/virtio/vhost.h
View File

@ -28,6 +28,12 @@ typedef unsigned long vhost_log_chunk_t;
#define VHOST_LOG_CHUNK (VHOST_LOG_PAGE * VHOST_LOG_BITS)
#define VHOST_INVALID_FEATURE_BIT (0xff)
struct vhost_log {
unsigned long long size;
int refcnt;
vhost_log_chunk_t log[0];
};
struct vhost_memory;
struct vhost_dev {
MemoryListener memory_listener;
@ -43,7 +49,6 @@ struct vhost_dev {
unsigned long long backend_features;
bool started;
bool log_enabled;
vhost_log_chunk_t *log;
unsigned long long log_size;
Error *migration_blocker;
bool force;
@ -52,6 +57,7 @@ struct vhost_dev {
hwaddr mem_changed_end_addr;
const VhostOps *vhost_ops;
void *opaque;
struct vhost_log *log;
};
int vhost_dev_init(struct vhost_dev *hdev, void *opaque,