virtio-blk dataplane currently creates/manages it's own thread to
offload work to a separate event loop.
This patch insteads allows us to specify a QContext-based event loop by
adding a "context" property for virtio-blk we can use like so:
qemu ... \
-object glib-qcontext,id=ctx0,threaded=yes
-drive file=file.raw,id=drive0,aio=native,cache=none \
-device virtio-blk,drive=drive0,scsi=off,x-data-plane=on,context=ctx0
virtio-blk dataplane then simply attachs/detaches it's AioContext to the
ctx0 event loop on start/stop.
This also makes available the option to drive a virtio-blk dataplane via
the default main loop:
qemu ... \
-drive file=file.raw,id=drive0,aio=native,cache=none \
-device virtio-blk,drive=drive0,scsi=off,x-data-plane=on,context=main
This doesn't do much in and of itself, but helps to demonstrate how we
might model a general mechanism to offload device workloads to separate
threads.
Signed-off-by: Michael Roth <mdr...@linux.vnet.ibm.com>
---
hw/block/dataplane/virtio-blk.c | 46 ++++++++++++---------------------------
include/hw/virtio/virtio-blk.h | 7 ++++--
2 files changed, 19 insertions(+), 34 deletions(-)
diff --git a/hw/block/dataplane/virtio-blk.c b/hw/block/dataplane/virtio-blk.c
index 0356665..08ea10f 100644
--- a/hw/block/dataplane/virtio-blk.c
+++ b/hw/block/dataplane/virtio-blk.c
@@ -24,6 +24,8 @@
#include "virtio-blk.h"
#include "block/aio.h"
#include "hw/virtio/virtio-bus.h"
+#include "qcontext/qcontext.h"
+#include "qcontext/glib-qcontext.h"
enum {
SEG_MAX = 126, /* maximum number of I/O segments */
@@ -60,6 +62,7 @@ struct VirtIOBlockDataPlane {
* use it).
*/
AioContext *ctx;
+ QContext *qctx;
EventNotifier io_notifier; /* Linux AIO completion */
EventNotifier host_notifier; /* doorbell */
@@ -375,26 +378,6 @@ static void handle_io(EventNotifier *e)
}
}
-static void *data_plane_thread(void *opaque)
-{
- VirtIOBlockDataPlane *s = opaque;
-
- do {
- aio_poll(s->ctx, true);
- } while (!s->stopping || s->num_reqs > 0);
- return NULL;
-}
-
-static void start_data_plane_bh(void *opaque)
-{
- VirtIOBlockDataPlane *s = opaque;
-
- qemu_bh_delete(s->start_bh);
- s->start_bh = NULL;
- qemu_thread_create(&s->thread, data_plane_thread,
- s, QEMU_THREAD_JOINABLE);
-}
-
bool virtio_blk_data_plane_create(VirtIODevice *vdev, VirtIOBlkConf *blk,
VirtIOBlockDataPlane **dataplane)
{
@@ -460,6 +443,7 @@ void virtio_blk_data_plane_start(VirtIOBlockDataPlane *s)
VirtioBusClass *k = VIRTIO_BUS_GET_CLASS(qbus);
VirtQueue *vq;
int i;
+ Error *err = NULL;
if (s->started) {
return;
@@ -502,9 +486,16 @@ void virtio_blk_data_plane_start(VirtIOBlockDataPlane *s)
/* Kick right away to begin processing requests already in vring */
event_notifier_set(virtio_queue_get_host_notifier(vq));
- /* Spawn thread in BH so it inherits iothread cpusets */
- s->start_bh = qemu_bh_new(start_data_plane_bh, s);
- qemu_bh_schedule(s->start_bh);
+ /* use QEMU main loop/context by default */
+ if (!s->blk->context) {
+ s->blk->context = g_strdup("main");
+ }
+ s->qctx = qcontext_find_by_name(s->blk->context, &err);
+ if (err) {
+ fprintf(stderr, "virtio-blk failed to start: %s",
error_get_pretty(err));
+ exit(1);
+ }
+ aio_context_attach(s->ctx, s->qctx);
}
void virtio_blk_data_plane_stop(VirtIOBlockDataPlane *s)
@@ -517,15 +508,6 @@ void virtio_blk_data_plane_stop(VirtIOBlockDataPlane *s)
s->stopping = true;
trace_virtio_blk_data_plane_stop(s);
- /* Stop thread or cancel pending thread creation BH */
- if (s->start_bh) {
- qemu_bh_delete(s->start_bh);
- s->start_bh = NULL;
- } else {
- aio_notify(s->ctx);
- qemu_thread_join(&s->thread);
- }
-
aio_set_event_notifier(s->ctx, &s->io_notifier, NULL, NULL);
ioq_cleanup(&s->ioqueue);
diff --git a/include/hw/virtio/virtio-blk.h b/include/hw/virtio/virtio-blk.h
index fc71853..c5514a4 100644
--- a/include/hw/virtio/virtio-blk.h
+++ b/include/hw/virtio/virtio-blk.h
@@ -110,6 +110,7 @@ struct VirtIOBlkConf
uint32_t scsi;
uint32_t config_wce;
uint32_t data_plane;
+ char *context;
};
struct VirtIOBlockDataPlane;
@@ -138,13 +139,15 @@ typedef struct VirtIOBlock {
DEFINE_BLOCK_CHS_PROPERTIES(_state, _field.conf), \
DEFINE_PROP_STRING("serial", _state, _field.serial), \
DEFINE_PROP_BIT("config-wce", _state, _field.config_wce, 0, true), \
- DEFINE_PROP_BIT("scsi", _state, _field.scsi, 0, true)
+ DEFINE_PROP_BIT("scsi", _state, _field.scsi, 0, true), \
+ DEFINE_PROP_STRING("context", _state, _field.context)
#else
#define DEFINE_VIRTIO_BLK_PROPERTIES(_state, _field) \
DEFINE_BLOCK_PROPERTIES(_state, _field.conf), \
DEFINE_BLOCK_CHS_PROPERTIES(_state, _field.conf), \
DEFINE_PROP_STRING("serial", _state, _field.serial), \
- DEFINE_PROP_BIT("config-wce", _state, _field.config_wce, 0, true)
+ DEFINE_PROP_BIT("config-wce", _state, _field.config_wce, 0, true), \
+ DEFINE_PROP_STRING("context", _state, _field.context)
#endif /* __linux__ */
void virtio_blk_set_conf(DeviceState *dev, VirtIOBlkConf *blk);
--
1.7.9.5
