lkml.org 
[lkml]   [2018]   [May]   [29]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [RFC v5 2/5] virtio_ring: support creating packed ring
On Tue, May 29, 2018 at 10:49:11AM +0800, Jason Wang wrote:
> On 2018年05月22日 16:16, Tiwei Bie wrote:
> > This commit introduces the support for creating packed ring.
> > All split ring specific functions are added _split suffix.
> > Some necessary stubs for packed ring are also added.
> >
> > Signed-off-by: Tiwei Bie <tiwei.bie@intel.com>
> > ---
> > drivers/virtio/virtio_ring.c | 801 +++++++++++++++++++++++------------
> > include/linux/virtio_ring.h | 8 +-
> > 2 files changed, 546 insertions(+), 263 deletions(-)
> >
> > diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
> > index 71458f493cf8..f5ef5f42a7cf 100644
> > --- a/drivers/virtio/virtio_ring.c
> > +++ b/drivers/virtio/virtio_ring.c
> > @@ -61,11 +61,15 @@ struct vring_desc_state {
> > struct vring_desc *indir_desc; /* Indirect descriptor, if any. */
> > };
> > +struct vring_desc_state_packed {
> > + int next; /* The next desc state. */
> > +};
> > +
> > struct vring_virtqueue {
> > struct virtqueue vq;
> > - /* Actual memory layout for this queue */
> > - struct vring vring;
> > + /* Is this a packed ring? */
> > + bool packed;
> > /* Can we use weak barriers? */
> > bool weak_barriers;
> > @@ -87,11 +91,39 @@ struct vring_virtqueue {
> > /* Last used index we've seen. */
> > u16 last_used_idx;
> > - /* Last written value to avail->flags */
> > - u16 avail_flags_shadow;
> > + union {
> > + /* Available for split ring */
> > + struct {
> > + /* Actual memory layout for this queue. */
> > + struct vring vring;
> > - /* Last written value to avail->idx in guest byte order */
> > - u16 avail_idx_shadow;
> > + /* Last written value to avail->flags */
> > + u16 avail_flags_shadow;
> > +
> > + /* Last written value to avail->idx in
> > + * guest byte order. */
> > + u16 avail_idx_shadow;
> > + };
> > +
> > + /* Available for packed ring */
> > + struct {
> > + /* Actual memory layout for this queue. */
> > + struct vring_packed vring_packed;
> > +
> > + /* Driver ring wrap counter. */
> > + u8 avail_wrap_counter;
> > +
> > + /* Device ring wrap counter. */
> > + u8 used_wrap_counter;
>
> How about just use boolean?

I can change it to bool if you want.

>
[...]
> > -static int vring_mapping_error(const struct vring_virtqueue *vq,
> > - dma_addr_t addr)
> > -{
> > - if (!vring_use_dma_api(vq->vq.vdev))
> > - return 0;
> > -
> > - return dma_mapping_error(vring_dma_dev(vq), addr);
> > -}
>
> It looks to me if you keep vring_mapping_error behind
> vring_unmap_one_split(), lots of changes were unncessary.
>
[...]
> > + }
> > + /* That should have freed everything. */
> > + BUG_ON(vq->vq.num_free != vq->vring.num);
> > +
> > + END_USE(vq);
> > + return NULL;
> > +}
>
> I think the those copy-and-paste hunks could be avoided and the diff should
> only contains renaming of the function. If yes, it would be very welcomed
> since it requires to compare the changes verbatim otherwise.

Michael suggested to lay out the code as:

XXX_split

XXX_packed

XXX wrappers

https://lkml.org/lkml/2018/4/13/410

That's why I moved some code.

>
> > +
> > +/*
> > + * The layout for the packed ring is a continuous chunk of memory
> > + * which looks like this.
> > + *
> > + * struct vring_packed {
> > + * // The actual descriptors (16 bytes each)
> > + * struct vring_packed_desc desc[num];
> > + *
> > + * // Padding to the next align boundary.
> > + * char pad[];
> > + *
> > + * // Driver Event Suppression
> > + * struct vring_packed_desc_event driver;
> > + *
> > + * // Device Event Suppression
> > + * struct vring_packed_desc_event device;
> > + * };
> > + */
> > +static inline void vring_init_packed(struct vring_packed *vr, unsigned int num,
> > + void *p, unsigned long align)
> > +{
> > + vr->num = num;
> > + vr->desc = p;
> > + vr->driver = (void *)(((uintptr_t)p + sizeof(struct vring_packed_desc)
> > + * num + align - 1) & ~(align - 1));
>
> If we choose not to go uapi, maybe we can use ALIGN() macro here?

Okay.

>
> > + vr->device = vr->driver + 1;
> > +}
[...]
> > +/* Only available for split ring */
> > const struct vring *virtqueue_get_vring(struct virtqueue *vq)
> > {
>
> A possible issue with this is:
>
> After commit d4674240f31f8c4289abba07d64291c6ddce51bc ("KVM: s390:
> virtio-ccw revision 1 SET_VQ"). CCW tries to use
> virtqueue_get_avail()/virtqueue_get_used(). Looks like a bug either here or
> ccw code.

Do we still need to support:

include/linux/virtio.h
/*
* Legacy accessors -- in almost all cases, these are the wrong functions
* to use.
*/
static inline void *virtqueue_get_desc(struct virtqueue *vq)
{
return virtqueue_get_vring(vq)->desc;
}
static inline void *virtqueue_get_avail(struct virtqueue *vq)
{
return virtqueue_get_vring(vq)->avail;
}
static inline void *virtqueue_get_used(struct virtqueue *vq)
{
return virtqueue_get_vring(vq)->used;
}

in packed ring?

If so, I think maybe it's better to expose them as
symbols and implement them in virtio_ring.c.

Best regards,
Tiwei Bie

\
 
 \ /
  Last update: 2018-05-29 07:24    [W:0.055 / U:8.840 seconds]
©2003-2018 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site