[PATCH 1/2] dma-buf: start caching of sg_table objects v2

[Daniel Vetter]

On Wed, May 15, 2019 at 11:25 AM Christian König
<ckoenig.leichtzumerken at gmail.com> wrote:
>
> Am 15.05.19 um 10:58 schrieb Daniel Vetter:
> > On Tue, May 14, 2019 at 04:05:14PM +0200, Christian König wrote:
> >> To allow a smooth transition from pinning buffer objects to dynamic
> >> invalidation we first start to cache the sg_table for an attachment.
> >>
> >> v2: keep closer to the DRM implementation
> >>
> >> Signed-off-by: Christian König <christian.koenig at amd.com>
> > i915 doesn't use the prime helpers, so this would be a change for us.
>
> Not a problem at all, see below. I've added an cache_sgt_mapping member
> into the dma_buf_ops structure. Only when this member is true the
> functionality is enabled.

Hm right I missed that.

> So I'm just moving code around in those two patches and no functional
> change at all.

Still not sure. I'll look at your latest dma-buf series to see how it
all fits together.
-Daniel

>
> Regards,
> Christian.
>
> >   Not
> > sure that matters. Since we can't use this as an easy way out of the
> > locking problem around reservation_object I'm not sure how useful it is to
> > move this ahead. At least until we have a clearer picture on how we plan
> > to roll out the dynamic dma-buf stuff. Once we have a bit more clarity
> > there I'm all for merging prep work, but as-is I'd be cautious ... This
> > stuff is a lot more tricky than it seems at first :-/
> > -Daniel
> >> ---
> >>   drivers/dma-buf/dma-buf.c | 27 +++++++++++++++++++++++++--
> >>   include/linux/dma-buf.h   | 13 +++++++++++++
> >>   2 files changed, 38 insertions(+), 2 deletions(-)
> >>
> >> diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c
> >> index 7c858020d14b..a2d34c6b80a5 100644
> >> --- a/drivers/dma-buf/dma-buf.c
> >> +++ b/drivers/dma-buf/dma-buf.c
> >> @@ -573,6 +573,7 @@ struct dma_buf_attachment *dma_buf_attach(struct dma_buf *dmabuf,
> >>      list_add(&attach->node, &dmabuf->attachments);
> >>
> >>      mutex_unlock(&dmabuf->lock);
> >> +
> >>      return attach;
> >>
> >>   err_attach:
> >> @@ -595,6 +596,9 @@ void dma_buf_detach(struct dma_buf *dmabuf, struct dma_buf_attachment *attach)
> >>      if (WARN_ON(!dmabuf || !attach))
> >>              return;
> >>
> >> +    if (attach->sgt)
> >> +            dmabuf->ops->unmap_dma_buf(attach, attach->sgt, attach->dir);
> >> +
> >>      mutex_lock(&dmabuf->lock);
> >>      list_del(&attach->node);
> >>      if (dmabuf->ops->detach)
> >> @@ -630,10 +634,27 @@ struct sg_table *dma_buf_map_attachment(struct dma_buf_attachment *attach,
> >>      if (WARN_ON(!attach || !attach->dmabuf))
> >>              return ERR_PTR(-EINVAL);
> >>
> >> +    if (attach->sgt) {
> >> +            /*
> >> +             * Two mappings with different directions for the same
> >> +             * attachment are not allowed.
> >> +             */
> >> +            if (attach->dir != direction &&
> >> +                attach->dir != DMA_BIDIRECTIONAL)
> >> +                    return ERR_PTR(-EBUSY);
> >> +
> >> +            return attach->sgt;
> >> +    }
> >> +
> >>      sg_table = attach->dmabuf->ops->map_dma_buf(attach, direction);
> >>      if (!sg_table)
> >>              sg_table = ERR_PTR(-ENOMEM);
> >>
> >> +    if (!IS_ERR(sg_table) && attach->dmabuf->ops->cache_sgt_mapping) {
> >> +            attach->sgt = sg_table;
> >> +            attach->dir = direction;
> >> +    }
> >> +
> >>      return sg_table;
> >>   }
> >>   EXPORT_SYMBOL_GPL(dma_buf_map_attachment);
> >> @@ -657,8 +678,10 @@ void dma_buf_unmap_attachment(struct dma_buf_attachment *attach,
> >>      if (WARN_ON(!attach || !attach->dmabuf || !sg_table))
> >>              return;
> >>
> >> -    attach->dmabuf->ops->unmap_dma_buf(attach, sg_table,
> >> -                                            direction);
> >> +    if (attach->sgt == sg_table)
> >> +            return;
> >> +
> >> +    attach->dmabuf->ops->unmap_dma_buf(attach, sg_table, direction);
> >>   }
> >>   EXPORT_SYMBOL_GPL(dma_buf_unmap_attachment);
> >>
> >> diff --git a/include/linux/dma-buf.h b/include/linux/dma-buf.h
> >> index 58725f890b5b..45b9767e67ec 100644
> >> --- a/include/linux/dma-buf.h
> >> +++ b/include/linux/dma-buf.h
> >> @@ -51,6 +51,15 @@ struct dma_buf_attachment;
> >>    * @vunmap: [optional] unmaps a vmap from the buffer
> >>    */
> >>   struct dma_buf_ops {
> >> +    /**
> >> +      * @cache_sgt_mapping:
> >> +      *
> >> +      * If true the framework will cache the first mapping made for each
> >> +      * attachment. This avoids creating mappings for attachments multiple
> >> +      * times.
> >> +      */
> >> +    bool cache_sgt_mapping;
> >> +
> >>      /**
> >>       * @attach:
> >>       *
> >> @@ -307,6 +316,8 @@ struct dma_buf {
> >>    * @dmabuf: buffer for this attachment.
> >>    * @dev: device attached to the buffer.
> >>    * @node: list of dma_buf_attachment.
> >> + * @sgt: cached mapping.
> >> + * @dir: direction of cached mapping.
> >>    * @priv: exporter specific attachment data.
> >>    *
> >>    * This structure holds the attachment information between the dma_buf buffer
> >> @@ -322,6 +333,8 @@ struct dma_buf_attachment {
> >>      struct dma_buf *dmabuf;
> >>      struct device *dev;
> >>      struct list_head node;
> >> +    struct sg_table *sgt;
> >> +    enum dma_data_direction dir;
> >>      void *priv;
> >>   };
> >>
> >> --
> >> 2.17.1
> >>
>


--
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch