Re: [PATCH] kvm tools: Use vring_need_event() to determine if interrupt is needed

Sasha Levin
2011-11-26T13:42:57Z

On Sat, 2011-11-26 at 14:40 +0200, Pekka Enberg wrote:
> On Fri, Nov 25, 2011 at 5:47 PM, Asias He <asias.hejun@gmail.com> wrote:
> > This patch also fixes fio seq-read hang problem.
> >
> > root@guest-kvm:~# cat seq-read.fio
> > [seq-read]
> > rw=read
> > bs=4096
> > size=512m
> > direct=1
> > filename=/dev/vdb
> >
> > root@guest-kvm:~# fio seq-read.fio
> > random-read: (g=0): rw=read, bs=4K-4K/4K-4K, ioengine=sync, iodepth=1
> > Starting 1 process
> > Jobs: 1 (f=1): [R] [50.0% done] [0K/0K /s] [0/0 iops] [eta 00m:27s]
> >
> > Signed-off-by: Asias He <asias.hejun@gmail.com>
>
> Sasha, does this look good to you?

I'm trying to see if it solved the hang problem I've mentioned on IRC.
Will update.
>
> > ---
> > tools/kvm/include/kvm/virtio.h | 6 ++----
> > tools/kvm/virtio/core.c | 16 ++++++++++++++++
> > 2 files changed, 18 insertions(+), 4 deletions(-)
> >
> > diff --git a/tools/kvm/include/kvm/virtio.h b/tools/kvm/include/kvm/virtio.h
> > index cd24285..d117bfc 100644
> > --- a/tools/kvm/include/kvm/virtio.h
> > +++ b/tools/kvm/include/kvm/virtio.h
> > @@ -22,6 +22,7 @@ struct virt_queue {
> > /* The last_avail_idx field is an index to ->ring of struct vring_avail.
> > It's where we assume the next request index is at. */
> > u16 last_avail_idx;
> > + u16 last_used_signalled;
> > };
> >
> > static inline u16 virt_queue__pop(struct virt_queue *queue)
> > @@ -53,13 +54,10 @@ static inline void *guest_pfn_to_host(struct kvm *kvm, u32 pfn)
> > return guest_flat_to_host(kvm, (unsigned long)pfn << VIRTIO_PCI_QUEUE_ADDR_SHIFT);
> > }
> >
> > -static inline int virtio_queue__should_signal(struct virt_queue *vq)
> > -{
> > - return vring_used_event(&vq->vring) <= vq->vring.used->idx;
> > -}
> >
> > struct vring_used_elem *virt_queue__set_used_elem(struct virt_queue *queue, u32 head, u32 len);
> >
> > +bool virtio_queue__should_signal(struct virt_queue *vq);
> > u16 virt_queue__get_iov(struct virt_queue *queue, struct iovec iov[], u16 *out, u16 *in, struct kvm *kvm);
> > u16 virt_queue__get_inout_iov(struct kvm *kvm, struct virt_queue *queue,
> > struct iovec in_iov[], struct iovec out_iov[],
> > diff --git a/tools/kvm/virtio/core.c b/tools/kvm/virtio/core.c
> > index 0466e07..8032d7a 100644
> > --- a/tools/kvm/virtio/core.c
> > +++ b/tools/kvm/virtio/core.c
> > @@ -109,3 +109,19 @@ int virtio__get_dev_specific_field(int offset, bool msix, bool features_hi, u32
> >
> > return VIRTIO_PCI_O_CONFIG;
> > }
> > +
> > +bool virtio_queue__should_signal(struct virt_queue *vq)
> > +{
> > + u16 old_idx, new_idx, event_idx;
> > +
> > + old_idx = vq->last_used_signalled;
> > + new_idx = vq->vring.used->idx;
> > + event_idx = vring_used_event(&vq->vring);
> > +
> > + if (vring_need_event(event_idx, new_idx, old_idx)) {
> > + vq->last_used_signalled = new_idx;
> > + return true;
> > + }
> > +
> > + return false;
> > +}
> > --
> > 1.7.7.3
> >
> > --
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> >

--

Sasha.