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virtio-blk: add iothread-vq-mapping parameter 
Add the iothread-vq-mapping parameter to assign virtqueues to IOThreads.
Store the vq:AioContext mapping in the new struct
VirtIOBlockDataPlane->vq_aio_context[] field and refactor the code to
use the per-vq AioContext instead of the BlockDriverState's AioContext.

Reimplement --device virtio-blk-pci,iothread= and non-IOThread mode by
assigning all virtqueues to the IOThread and main loop's AioContext in
vq_aio_context[], respectively.

The comment in struct VirtIOBlockDataPlane about EventNotifiers is
stale. Remove it.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Message-ID: <20231220134755.814917-5-stefanha@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
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Stefan Hajnoczi authored and Kevin Wolf committed Dec 21, 2023
1 parent 050dc39 commit ec25ed8
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Showing 4 changed files with 202 additions and 50 deletions.
155 changes: 117 additions & 38 deletions hw/block/dataplane/virtio-blk.c
View file
Expand Up @@ -32,13 +32,11 @@ struct VirtIOBlockDataPlane {
VirtIOBlkConf *conf;
VirtIODevice *vdev;

/* Note that these EventNotifiers are assigned by value. This is
* fine as long as you do not call event_notifier_cleanup on them
* (because you don't own the file descriptor or handle; you just
* use it).
/*
* The AioContext for each virtqueue. The BlockDriverState will use the
* first element as its AioContext.
*/
IOThread *iothread;
AioContext *ctx;
AioContext **vq_aio_context;
};

/* Raise an interrupt to signal guest, if necessary */
Expand All @@ -47,6 +45,45 @@ void virtio_blk_data_plane_notify(VirtIOBlockDataPlane *s, VirtQueue *vq)
virtio_notify_irqfd(s->vdev, vq);
}

/* Generate vq:AioContext mappings from a validated iothread-vq-mapping list */
static void
apply_vq_mapping(IOThreadVirtQueueMappingList *iothread_vq_mapping_list,
AioContext **vq_aio_context, uint16_t num_queues)
{
IOThreadVirtQueueMappingList *node;
size_t num_iothreads = 0;
size_t cur_iothread = 0;

for (node = iothread_vq_mapping_list; node; node = node->next) {
num_iothreads++;
}

for (node = iothread_vq_mapping_list; node; node = node->next) {
IOThread *iothread = iothread_by_id(node->value->iothread);
AioContext *ctx = iothread_get_aio_context(iothread);

/* Released in virtio_blk_data_plane_destroy() */
object_ref(OBJECT(iothread));

if (node->value->vqs) {
uint16List *vq;

/* Explicit vq:IOThread assignment */
for (vq = node->value->vqs; vq; vq = vq->next) {
vq_aio_context[vq->value] = ctx;
}
} else {
/* Round-robin vq:IOThread assignment */
for (unsigned i = cur_iothread; i < num_queues;
i += num_iothreads) {
vq_aio_context[i] = ctx;
}
}

cur_iothread++;
}
}

/* Context: QEMU global mutex held */
bool virtio_blk_data_plane_create(VirtIODevice *vdev, VirtIOBlkConf *conf,
VirtIOBlockDataPlane **dataplane,
Expand All @@ -58,7 +95,7 @@ bool virtio_blk_data_plane_create(VirtIODevice *vdev, VirtIOBlkConf *conf,

*dataplane = NULL;

if (conf->iothread) {
if (conf->iothread || conf->iothread_vq_mapping_list) {
if (!k->set_guest_notifiers || !k->ioeventfd_assign) {
error_setg(errp,
"device is incompatible with iothread "
Expand Down Expand Up @@ -86,13 +123,24 @@ bool virtio_blk_data_plane_create(VirtIODevice *vdev, VirtIOBlkConf *conf,
s = g_new0(VirtIOBlockDataPlane, 1);
s->vdev = vdev;
s->conf = conf;
s->vq_aio_context = g_new(AioContext *, conf->num_queues);

if (conf->iothread_vq_mapping_list) {
apply_vq_mapping(conf->iothread_vq_mapping_list, s->vq_aio_context,
conf->num_queues);
} else if (conf->iothread) {
AioContext *ctx = iothread_get_aio_context(conf->iothread);
for (unsigned i = 0; i < conf->num_queues; i++) {
s->vq_aio_context[i] = ctx;
}

if (conf->iothread) {
s->iothread = conf->iothread;
object_ref(OBJECT(s->iothread));
s->ctx = iothread_get_aio_context(s->iothread);
/* Released in virtio_blk_data_plane_destroy() */
object_ref(OBJECT(conf->iothread));
} else {
s->ctx = qemu_get_aio_context();
AioContext *ctx = qemu_get_aio_context();
for (unsigned i = 0; i < conf->num_queues; i++) {
s->vq_aio_context[i] = ctx;
}
}

*dataplane = s;
Expand All @@ -104,16 +152,29 @@ bool virtio_blk_data_plane_create(VirtIODevice *vdev, VirtIOBlkConf *conf,
void virtio_blk_data_plane_destroy(VirtIOBlockDataPlane *s)
{
VirtIOBlock *vblk;
VirtIOBlkConf *conf = s->conf;

if (!s) {
return;
}

vblk = VIRTIO_BLK(s->vdev);
assert(!vblk->dataplane_started);
if (s->iothread) {
object_unref(OBJECT(s->iothread));

if (conf->iothread_vq_mapping_list) {
IOThreadVirtQueueMappingList *node;

for (node = conf->iothread_vq_mapping_list; node; node = node->next) {
IOThread *iothread = iothread_by_id(node->value->iothread);
object_unref(OBJECT(iothread));
}
}

if (conf->iothread) {
object_unref(OBJECT(conf->iothread));
}

g_free(s->vq_aio_context);
g_free(s);
}

Expand Down Expand Up @@ -177,19 +238,13 @@ int virtio_blk_data_plane_start(VirtIODevice *vdev)

trace_virtio_blk_data_plane_start(s);

r = blk_set_aio_context(s->conf->conf.blk, s->ctx, &local_err);
r = blk_set_aio_context(s->conf->conf.blk, s->vq_aio_context[0],
&local_err);
if (r < 0) {
error_report_err(local_err);
goto fail_aio_context;
}

/* Kick right away to begin processing requests already in vring */
for (i = 0; i < nvqs; i++) {
VirtQueue *vq = virtio_get_queue(s->vdev, i);

event_notifier_set(virtio_queue_get_host_notifier(vq));
}

/*
* These fields must be visible to the IOThread when it processes the
* virtqueue, otherwise it will think dataplane has not started yet.
Expand All @@ -206,8 +261,12 @@ int virtio_blk_data_plane_start(VirtIODevice *vdev)
if (!blk_in_drain(s->conf->conf.blk)) {
for (i = 0; i < nvqs; i++) {
VirtQueue *vq = virtio_get_queue(s->vdev, i);
AioContext *ctx = s->vq_aio_context[i];

virtio_queue_aio_attach_host_notifier(vq, s->ctx);
/* Kick right away to begin processing requests already in vring */
event_notifier_set(virtio_queue_get_host_notifier(vq));

virtio_queue_aio_attach_host_notifier(vq, ctx);
}
}
return 0;
Expand Down Expand Up @@ -236,23 +295,18 @@ int virtio_blk_data_plane_start(VirtIODevice *vdev)
*
* Context: BH in IOThread
*/
static void virtio_blk_data_plane_stop_bh(void *opaque)
static void virtio_blk_data_plane_stop_vq_bh(void *opaque)
{
VirtIOBlockDataPlane *s = opaque;
unsigned i;

for (i = 0; i < s->conf->num_queues; i++) {
VirtQueue *vq = virtio_get_queue(s->vdev, i);
EventNotifier *host_notifier = virtio_queue_get_host_notifier(vq);
VirtQueue *vq = opaque;
EventNotifier *host_notifier = virtio_queue_get_host_notifier(vq);

virtio_queue_aio_detach_host_notifier(vq, s->ctx);
virtio_queue_aio_detach_host_notifier(vq, qemu_get_current_aio_context());

/*
* Test and clear notifier after disabling event, in case poll callback
* didn't have time to run.
*/
virtio_queue_host_notifier_read(host_notifier);
}
/*
* Test and clear notifier after disabling event, in case poll callback
* didn't have time to run.
*/
virtio_queue_host_notifier_read(host_notifier);
}

/* Context: QEMU global mutex held */
Expand All @@ -279,7 +333,12 @@ void virtio_blk_data_plane_stop(VirtIODevice *vdev)
trace_virtio_blk_data_plane_stop(s);

if (!blk_in_drain(s->conf->conf.blk)) {
aio_wait_bh_oneshot(s->ctx, virtio_blk_data_plane_stop_bh, s);
for (i = 0; i < nvqs; i++) {
VirtQueue *vq = virtio_get_queue(s->vdev, i);
AioContext *ctx = s->vq_aio_context[i];

aio_wait_bh_oneshot(ctx, virtio_blk_data_plane_stop_vq_bh, vq);
}
}

/*
Expand Down Expand Up @@ -322,3 +381,23 @@ void virtio_blk_data_plane_stop(VirtIODevice *vdev)

s->stopping = false;
}

void virtio_blk_data_plane_detach(VirtIOBlockDataPlane *s)
{
VirtIODevice *vdev = VIRTIO_DEVICE(s->vdev);

for (uint16_t i = 0; i < s->conf->num_queues; i++) {
VirtQueue *vq = virtio_get_queue(vdev, i);
virtio_queue_aio_detach_host_notifier(vq, s->vq_aio_context[i]);
}
}

void virtio_blk_data_plane_attach(VirtIOBlockDataPlane *s)
{
VirtIODevice *vdev = VIRTIO_DEVICE(s->vdev);

for (uint16_t i = 0; i < s->conf->num_queues; i++) {
VirtQueue *vq = virtio_get_queue(vdev, i);
virtio_queue_aio_attach_host_notifier(vq, s->vq_aio_context[i]);
}
}
3 changes: 3 additions & 0 deletions hw/block/dataplane/virtio-blk.h
View file
Expand Up @@ -28,4 +28,7 @@ void virtio_blk_data_plane_notify(VirtIOBlockDataPlane *s, VirtQueue *vq);
int virtio_blk_data_plane_start(VirtIODevice *vdev);
void virtio_blk_data_plane_stop(VirtIODevice *vdev);

void virtio_blk_data_plane_detach(VirtIOBlockDataPlane *s);
void virtio_blk_data_plane_attach(VirtIOBlockDataPlane *s);

#endif /* HW_DATAPLANE_VIRTIO_BLK_H */
92 changes: 80 additions & 12 deletions hw/block/virtio-blk.c
View file
Expand Up @@ -1151,6 +1151,7 @@ static void virtio_blk_handle_output(VirtIODevice *vdev, VirtQueue *vq)
return;
}
}

virtio_blk_handle_vq(s, vq);
}

Expand Down Expand Up @@ -1463,6 +1464,68 @@ static int virtio_blk_load_device(VirtIODevice *vdev, QEMUFile *f,
return 0;
}

static bool
validate_iothread_vq_mapping_list(IOThreadVirtQueueMappingList *list,
uint16_t num_queues, Error **errp)
{
g_autofree unsigned long *vqs = bitmap_new(num_queues);
g_autoptr(GHashTable) iothreads =
g_hash_table_new(g_str_hash, g_str_equal);

for (IOThreadVirtQueueMappingList *node = list; node; node = node->next) {
const char *name = node->value->iothread;
uint16List *vq;

if (!iothread_by_id(name)) {
error_setg(errp, "IOThread \"%s\" object does not exist", name);
return false;
}

if (!g_hash_table_add(iothreads, (gpointer)name)) {
error_setg(errp,
"duplicate IOThread name \"%s\" in iothread-vq-mapping",
name);
return false;
}

if (node != list) {
if (!!node->value->vqs != !!list->value->vqs) {
error_setg(errp, "either all items in iothread-vq-mapping "
"must have vqs or none of them must have it");
return false;
}
}

for (vq = node->value->vqs; vq; vq = vq->next) {
if (vq->value >= num_queues) {
error_setg(errp, "vq index %u for IOThread \"%s\" must be "
"less than num_queues %u in iothread-vq-mapping",
vq->value, name, num_queues);
return false;
}

if (test_and_set_bit(vq->value, vqs)) {
error_setg(errp, "cannot assign vq %u to IOThread \"%s\" "
"because it is already assigned", vq->value, name);
return false;
}
}
}

if (list->value->vqs) {
for (uint16_t i = 0; i < num_queues; i++) {
if (!test_bit(i, vqs)) {
error_setg(errp,
"missing vq %u IOThread assignment in iothread-vq-mapping",
i);
return false;
}
}
}

return true;
}

static void virtio_resize_cb(void *opaque)
{
VirtIODevice *vdev = opaque;
Expand All @@ -1487,34 +1550,24 @@ static void virtio_blk_resize(void *opaque)
static void virtio_blk_drained_begin(void *opaque)
{
VirtIOBlock *s = opaque;
VirtIODevice *vdev = VIRTIO_DEVICE(opaque);
AioContext *ctx = blk_get_aio_context(s->conf.conf.blk);

if (!s->dataplane || !s->dataplane_started) {
return;
}

for (uint16_t i = 0; i < s->conf.num_queues; i++) {
VirtQueue *vq = virtio_get_queue(vdev, i);
virtio_queue_aio_detach_host_notifier(vq, ctx);
}
virtio_blk_data_plane_detach(s->dataplane);
}

/* Resume virtqueue ioeventfd processing after drain */
static void virtio_blk_drained_end(void *opaque)
{
VirtIOBlock *s = opaque;
VirtIODevice *vdev = VIRTIO_DEVICE(opaque);
AioContext *ctx = blk_get_aio_context(s->conf.conf.blk);

if (!s->dataplane || !s->dataplane_started) {
return;
}

for (uint16_t i = 0; i < s->conf.num_queues; i++) {
VirtQueue *vq = virtio_get_queue(vdev, i);
virtio_queue_aio_attach_host_notifier(vq, ctx);
}
virtio_blk_data_plane_attach(s->dataplane);
}

static const BlockDevOps virtio_block_ops = {
Expand Down Expand Up @@ -1600,6 +1653,19 @@ static void virtio_blk_device_realize(DeviceState *dev, Error **errp)
return;
}

if (conf->iothread_vq_mapping_list) {
if (conf->iothread) {
error_setg(errp, "iothread and iothread-vq-mapping properties "
"cannot be set at the same time");
return;
}

if (!validate_iothread_vq_mapping_list(conf->iothread_vq_mapping_list,
conf->num_queues, errp)) {
return;
}
}

s->config_size = virtio_get_config_size(&virtio_blk_cfg_size_params,
s->host_features);
virtio_init(vdev, VIRTIO_ID_BLOCK, s->config_size);
Expand Down Expand Up @@ -1702,6 +1768,8 @@ static Property virtio_blk_properties[] = {
DEFINE_PROP_BOOL("seg-max-adjust", VirtIOBlock, conf.seg_max_adjust, true),
DEFINE_PROP_LINK("iothread", VirtIOBlock, conf.iothread, TYPE_IOTHREAD,
IOThread *),
DEFINE_PROP_IOTHREAD_VQ_MAPPING_LIST("iothread-vq-mapping", VirtIOBlock,
conf.iothread_vq_mapping_list),
DEFINE_PROP_BIT64("discard", VirtIOBlock, host_features,
VIRTIO_BLK_F_DISCARD, true),
DEFINE_PROP_BOOL("report-discard-granularity", VirtIOBlock,
Expand Down

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