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vhost-vdpa: Do not send empty IOTLB update batches 

With the introduction of the batch hinting, meaningless batches can be
created with no IOTLB updates if the memory region was skipped by
vhost_vdpa_listener_skipped_section. This is the case of host notifiers
memory regions, device un/realize, and others. This causes the vdpa
device to receive dma mapping settings with no changes, a possibly
expensive operation for nothing.

To avoid that, VHOST_IOTLB_BATCH_BEGIN hint is delayed until we have a
meaningful (not skipped section) mapping or unmapping operation, and
VHOST_IOTLB_BATCH_END is not written unless at least one of _UPDATE /
_INVALIDATE has been issued.

v3:
  * Use a bool instead of a counter avoiding potential number wrapping
  * Fix bad check on _commit
  * Move VHOST_BACKEND_F_IOTLB_BATCH check to
    vhost_vdpa_iotlb_batch_begin_once

v2 (from RFC):
  * Rename misleading name
  * Abstract start batching function for listener_add/del

Signed-off-by: Eugenio Pérez <eperezma@redhat.com>
Message-Id: <20210812140933.226288-1-eperezma@redhat.com>
Acked-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:
Eugenio Pérez 2021-08-12 16:09:33 +02:00 committed by Michael S. Tsirkin
parent 8880cc4362
commit e6db5df7e2
2 changed files with 24 additions and 12 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

35
hw/virtio/vhost-vdpa.c
View File

@ -89,19 +89,13 @@ static int vhost_vdpa_dma_unmap(struct vhost_vdpa *v, hwaddr iova,
return ret;
}
static void vhost_vdpa_listener_begin(MemoryListener *listener)
static void vhost_vdpa_listener_begin_batch(struct vhost_vdpa *v)
{
struct vhost_vdpa *v = container_of(listener, struct vhost_vdpa, listener);
struct vhost_dev *dev = v->dev;
struct vhost_msg_v2 msg = {};
int fd = v->device_fd;
if (!(dev->backend_cap & (0x1ULL << VHOST_BACKEND_F_IOTLB_BATCH))) {
return;
}
msg.type = v->msg_type;
msg.iotlb.type = VHOST_IOTLB_BATCH_BEGIN;
struct vhost_msg_v2 msg = {
.type = v->msg_type,
.iotlb.type = VHOST_IOTLB_BATCH_BEGIN,
};
if (write(fd, &msg, sizeof(msg)) != sizeof(msg)) {
error_report("failed to write, fd=%d, errno=%d (%s)",
@ -109,6 +103,16 @@ static void vhost_vdpa_listener_begin(MemoryListener *listener)
}
}
static void vhost_vdpa_iotlb_batch_begin_once(struct vhost_vdpa *v)
{
if (v->dev->backend_cap & (0x1ULL << VHOST_BACKEND_F_IOTLB_BATCH) &&
!v->iotlb_batch_begin_sent) {
vhost_vdpa_listener_begin_batch(v);
}
v->iotlb_batch_begin_sent = true;
}
static void vhost_vdpa_listener_commit(MemoryListener *listener)
{
struct vhost_vdpa *v = container_of(listener, struct vhost_vdpa, listener);
@ -120,6 +124,10 @@ static void vhost_vdpa_listener_commit(MemoryListener *listener)
return;
}
if (!v->iotlb_batch_begin_sent) {
return;
}
msg.type = v->msg_type;
msg.iotlb.type = VHOST_IOTLB_BATCH_END;
@ -127,6 +135,8 @@ static void vhost_vdpa_listener_commit(MemoryListener *listener)
error_report("failed to write, fd=%d, errno=%d (%s)",
fd, errno, strerror(errno));
}
v->iotlb_batch_begin_sent = false;
}
static void vhost_vdpa_listener_region_add(MemoryListener *listener,
@ -170,6 +180,7 @@ static void vhost_vdpa_listener_region_add(MemoryListener *listener,
llsize = int128_sub(llend, int128_make64(iova));
vhost_vdpa_iotlb_batch_begin_once(v);
ret = vhost_vdpa_dma_map(v, iova, int128_get64(llsize),
vaddr, section->readonly);
if (ret) {
@ -221,6 +232,7 @@ static void vhost_vdpa_listener_region_del(MemoryListener *listener,
llsize = int128_sub(llend, int128_make64(iova));
vhost_vdpa_iotlb_batch_begin_once(v);
ret = vhost_vdpa_dma_unmap(v, iova, int128_get64(llsize));
if (ret) {
error_report("vhost_vdpa dma unmap error!");
@ -234,7 +246,6 @@ static void vhost_vdpa_listener_region_del(MemoryListener *listener,
* depends on the addnop().
*/
static const MemoryListener vhost_vdpa_memory_listener = {
.begin = vhost_vdpa_listener_begin,
.commit = vhost_vdpa_listener_commit,
.region_add = vhost_vdpa_listener_region_add,
.region_del = vhost_vdpa_listener_region_del,

1
include/hw/virtio/vhost-vdpa.h
View File

@ -22,6 +22,7 @@ typedef struct VhostVDPAHostNotifier {
typedef struct vhost_vdpa {
int device_fd;
uint32_t msg_type;
bool iotlb_batch_begin_sent;
MemoryListener listener;
struct vhost_dev *dev;
VhostVDPAHostNotifier notifier[VIRTIO_QUEUE_MAX];