On 06/04/2015 06:44 PM, Michael S. Tsirkin wrote:
> On Thu, Jun 04, 2015 at 05:28:46AM -0400, Jason Wang wrote:
>> > 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 <m...@redhat.com>
>> > Signed-off-by: Jason Wang <jasow...@redhat.com>
>> > ---
>> > Changes from V4:
>> > - leave a dummy vhost_log structure if log size is zero
>> > - use vhost_log_put() to sync in vhost_dev_stop()
>> > Changes from V3:
>> > - Only sync the old log on put
>> > Changes from V2:
>> > - rebase to HEAD
>> > - drop unused node field from vhost_log structure
>> > Changes from V1:
>> > - Drop the list of vhost log, instead, using a global pointer instead
>> > ---
>> > hw/virtio/vhost.c | 77
>> > ++++++++++++++++++++++++++++++++++++-----------
>> > include/hw/virtio/vhost.h | 8 ++++-
>> > 2 files changed, 66 insertions(+), 19 deletions(-)
>> >
>> > diff --git a/hw/virtio/vhost.c b/hw/virtio/vhost.c
>> > index 54851b7..01f1e04 100644
>> > --- a/hw/virtio/vhost.c
>> > +++ b/hw/virtio/vhost.c
>> > @@ -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) {
> OK this one now can be unconditional, right?
> I'll apply as is, pls fix with a patch on top.
>
Right. Ok.
