On Tue, 11/11 10:29, Ming Lei wrote:
> On Tue, Nov 11, 2014 at 9:52 AM, Fam Zheng <f...@redhat.com> wrote:
> > On Tue, 11/11 09:17, Ming Lei wrote:
> >> It isn't necessery to notify guest each time when one request
> >> is completed, and it should be enough to just notify one time
> >> for each running of virtio_scsi_iothread_handle_cmd().
> >>
> >> This patch supresses about 30K/sec write on eventfd.
> >>
> >> Signed-off-by: Ming Lei <ming....@canonical.com>
> >> ---
> >> hw/scsi/virtio-scsi-dataplane.c | 4 +++-
> >> hw/scsi/virtio-scsi.c | 26 +++++++++++++++++++++++++-
> >> include/hw/virtio/virtio-scsi.h | 4 ++++
> >> 3 files changed, 32 insertions(+), 2 deletions(-)
> >>
> >> diff --git a/hw/scsi/virtio-scsi-dataplane.c
> >> b/hw/scsi/virtio-scsi-dataplane.c
> >> index df17229..294515a 100644
> >> --- a/hw/scsi/virtio-scsi-dataplane.c
> >> +++ b/hw/scsi/virtio-scsi-dataplane.c
> >> @@ -62,6 +62,7 @@ static VirtIOSCSIVring
> >> *virtio_scsi_vring_init(VirtIOSCSI *s,
> >> aio_set_event_notifier(s->ctx, &r->host_notifier, handler);
> >>
> >> r->parent = s;
> >> + r->qid = n;
> >>
> >> if (!vring_setup(&r->vring, VIRTIO_DEVICE(s), n)) {
> >> fprintf(stderr, "virtio-scsi: VRing setup failed\n");
> >> @@ -95,7 +96,8 @@ void virtio_scsi_vring_push_notify(VirtIOSCSIReq *req)
> >> {
> >> vring_push(&req->vring->vring, &req->elem,
> >> req->qsgl.size + req->resp_iov.size);
> >> - event_notifier_set(&req->vring->guest_notifier);
> >> + req->dev->pending_guest_notify |= 1 << (req->vring->qid - 2);
> >> + qemu_bh_schedule(req->dev->guest_notify_bh);
> >> }
> >>
> >> static void virtio_scsi_iothread_handle_ctrl(EventNotifier *notifier)
> >> diff --git a/hw/scsi/virtio-scsi.c b/hw/scsi/virtio-scsi.c
> >> index 6e34a2c..98411ef 100644
> >> --- a/hw/scsi/virtio-scsi.c
> >> +++ b/hw/scsi/virtio-scsi.c
> >> @@ -86,6 +86,21 @@ static void virtio_scsi_complete_req(VirtIOSCSIReq *req)
> >> virtio_scsi_free_req(req);
> >> }
> >>
> >> +static void notify_guest_bh(void *opaque)
> >> +{
> >> + VirtIOSCSI *s = opaque;
> >> + unsigned int qid;
> >> + uint64_t pending = s->pending_guest_notify;
> >> +
> >> + s->pending_guest_notify = 0;
> >> +
> >> + while ((qid = ffsl(pending))) {
> >> + qid--;
> >> + event_notifier_set(&s->cmd_vrings[qid]->guest_notifier);
> >
> > Don't we need to handle ctrlq and eventq as well?
>
> Most of times no frequent activity in ctrl and event vq, so it isn't
> necessary to make them involved.
I mean virtio_scsi_vring_push_notify is not only used to notify cmd, it should
also work for ctrl and event, because its caller virtio_scsi_complete_req is
also called in virtio_scsi_handle_ctrl_req and virtio_scsi_push_event.
>
> >
> >> + pending &= ~(1 << qid);
> >> + }
> >> +}
> >> +
> >> static void virtio_scsi_bad_req(void)
> >> {
> >> error_report("wrong size for virtio-scsi headers");
> >> @@ -824,7 +839,12 @@ void virtio_scsi_common_realize(DeviceState *dev,
> >> Error **errp,
> >> }
> >>
> >> if (s->conf.iothread) {
> >> - virtio_scsi_set_iothread(VIRTIO_SCSI(s), s->conf.iothread);
> >> + VirtIOSCSI *vis = VIRTIO_SCSI(s);
> >> +
> >> + QEMU_BUILD_BUG_ON(VIRTIO_PCI_QUEUE_MAX > 64);
> >> + virtio_scsi_set_iothread(vis, s->conf.iothread);
> >> + vis->pending_guest_notify = 0;
> >> + vis->guest_notify_bh = aio_bh_new(vis->ctx, notify_guest_bh, vis);
> >> }
> >> }
> >>
> >> @@ -901,7 +921,11 @@ void virtio_scsi_common_unrealize(DeviceState *dev,
> >> Error **errp)
> >> {
> >> VirtIODevice *vdev = VIRTIO_DEVICE(dev);
> >> VirtIOSCSICommon *vs = VIRTIO_SCSI_COMMON(dev);
> >> + VirtIOSCSI *s = VIRTIO_SCSI(vs);
> >>
> >> + if (vs->conf.iothread) {
> >> + qemu_bh_delete(s->guest_notify_bh);
> >> + }
> >> g_free(vs->cmd_vqs);
> >> virtio_cleanup(vdev);
> >> }
> >> diff --git a/include/hw/virtio/virtio-scsi.h
> >> b/include/hw/virtio/virtio-scsi.h
> >> index 9e1a49c..5e6c57e 100644
> >> --- a/include/hw/virtio/virtio-scsi.h
> >> +++ b/include/hw/virtio/virtio-scsi.h
> >> @@ -163,6 +163,7 @@ typedef struct {
> >> Vring vring;
> >> EventNotifier host_notifier;
> >> EventNotifier guest_notifier;
> >> + uint32_t qid;
> >
> > Could this "bool notify_pending"? In this case pending_guest_notify in
> > VirtIOSCSI is not necessary. I guess looking into no more than 64
> > VirtIOSCSIVring elements in guest_notify_bh is not _that_ expensive so it's
> > not
> > worth the complexity.
>
> We need to know which queue the pending notifier is sent to in BH
> handler, and 64 is the limit for queue number, not element number.
>
> Actually it is a bit expensive, and 30K/sec write syscall is wasted in
> the unnecessary & repeated notifying.
>
> And the similar approach is applied in virtio-blk dataplane too, :-)
>
I mean something like:
diff --git a/include/hw/virtio/virtio-scsi.h b/include/hw/virtio/virtio-scsi.h
index 9e1a49c..5e6c57e 100644
--- a/include/hw/virtio/virtio-scsi.h
+++ b/include/hw/virtio/virtio-scsi.h
@@ -163,6 +163,7 @@ typedef struct {
Vring vring;
EventNotifier host_notifier;
EventNotifier guest_notifier;
+ bool notify_pending;
@@ -95,7 +96,8 @@ void virtio_scsi_vring_push_notify(VirtIOSCSIReq *req)
{
vring_push(&req->vring->vring, &req->elem,
req->qsgl.size + req->resp_iov.size);
- event_notifier_set(&req->vring->guest_notifier);
+ req->vring->pending_notify = true;
+ qemu_bh_schedule(req->dev->guest_notify_bh);
}
And in notify_guest_bh you go through all the vrings and call
event_notifier_set on those with vring->pending_notify == true.
Fam
