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

Pekka Enberg
2011-11-26T12:40:18Z

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?

> ---
>  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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